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Cottonmouth (Water Moccasin) - Agkistrodon piscivorus
Scalesofanubis Wrote:Cottonmouth (Water Moccasin) - Agkistrodon piscivorus

[Image: tumblr_nil8j2arpN1tkalkoo1_500.jpg]

Scientific classification
Kingdom:  Animalia
Phylum:  Chordata
Class:  Reptilia
Order:  Squamata
Suborder:  Serpentes
Family:  Viperidae
Subfamily:  Crotalinae
Genus:  Agkistrodon
Species:  Agkistrodon piscivorus

Agkistrodon piscivorus is a venomous snake, a species of pit viper, found in the southeastern USA. Adults are large and capable of delivering a painful and potentially fatal bite. When antagonized, they will stand their ground by coiling their bodies and displaying their fangs. Although their aggression has been exaggerated, on rare occasions territorial males will approach intruders in an aggressive manner. This is the world's only semiaquatic viper, usually found in or near water, particularly in slow-moving and shallow lakes, streams, and marshes. The snake is a strong swimmer and will even enter the sea, successfully colonizing islands off both the Atlantic and Gulf coasts. The generic name is derived from the Greek words ancistro (hooked) and odon (tooth), and the species name comes from the Latin piscis (fish) and voro (to eat); thus, the scientific name translates into “hooked-tooth fish-eater”.  Common names include variants on water moccasin, swamp moccasin or black moccasin; also cottonmouth, gapper, or simply viper. Many of the common names refer to the threat display, where this species will often stand its ground and gape at an intruder, exposing the white lining of its mouth. Three subspecies are currently recognized, including the nominate subspecies described here. Its diet consists mainly of fish and frogs, but is otherwise highly varied and, uniquely, has even been reported to include carrion.

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This is the largest species of the genus Agkistrodon. Adults commonly exceed 80 cm (31.5 in) in length, females grow smaller than males. Occasionally, individuals may exceed 180 cm (71 in) in length, especially in the eastern part of the range. According to Gloyd and Conant (1990), the largest recorded specimen of A. p. piscivorus was 188 cm (74 in) in length, based on a specimen caught in the Dismal Swamp region and given to the Philadelphia Zoological Garden. It should be noted, however, that this snake had apparently been injured during capture, died several days later and was measured when straight and relaxed.
The broad head is distinct from the neck, and the snout is blunt in profile with the rim of the top of the head extending forwards slightly further than the mouth. Substantial cranial plates are present, although the parietal plates are often fragmented, especially towards the rear. A loreal scale is absent. There are six to 9 supralabials and eight to 12 infralabials. At midbody, there are 23-27 rows of dorsal scales. All dorsal scale rows have keels, although those on the lowermost scale rows are weak. In males/females, the ventral scales number 130-145/128-144 and the subcaudals 38-54/36-50. Many of the latter may be divided.
Though the majority of specimens are almost or even totally black, (with the exception of head and facial markings), the color pattern may consist of a brown, gray, tan, yellowish-olive or blackish ground color, which is overlaid with a series of 10-17 dark brown to almost black crossbands. These crossbands, which usually have black edges, are sometimes broken along the dorsal midline to form a series of staggered halfbands on either side of the body. These crossbands are visibly lighter in the center, almost matching the ground color, often contain irregular dark markings, and extend well down onto the ventral scales. The dorsal banding pattern fades with age, so older individuals are an almost uniform olive brown, grayish-brown or black. The belly is white, yellowish-white or tan, marked with dark spots, and becomes darker posteriorly. The amount of dark pigment on the belly varies from virtually nothing to almost completely black. The head is a more or less uniform brown color, especially in A. p. piscivorus. Subadult specimens may exhibit the same kind of dark, parietal spots characteristic of A. contortrix, but sometimes these are still visible in adults. Eastern populations have a broad, dark, postocular stripe, bordered with pale pigment above and below, that is faint or absent in western populations. The underside of the head is generally whitish, cream or tan.
Juvenile and subadult specimens generally have a more contrasting color pattern, with dark crossbands on a lighter ground color. The ground color is then tan, brown or reddish brown. The tip of the tail is usually yellowish, becoming greenish yellow or greenish in subadults, and then black in adults. On some juveniles, the banding pattern can also be seen on the tail. 
This species is often confused with the copperhead, A. contortrix. This is especially true for juveniles, but there are differences. A. piscivorus has broad, dark stripes on the sides of its head that extend back from the eye, whereas A. contortrix has only a thin dark line that divides the pale supralabials from the somewhat darker color of the head The watersnakes of the genus Nerodia are also similar in appearance, being thick-bodied with large heads, but they have round pupils, no loreal pit, a single anal plate, subcaudal scales that are divided throughout and a distinctive overall color pattern.

[Image: cottonmouth7785.jpg]

Range and Habitat
This species is found in the eastern USA from Virginia, south through the Florida peninsula and west to Arkansas, eastern and southern Oklahoma, Georgia lakes such as Lanier, Oconee, Hartwell,and Seminole, and east and central Texas. A few records exist of the species being found along the Rio Grande in Texas, but these are thought to represent disjunct populations, now possibly eradicated. The type locality given is "Carolina", although Schmidt (1953) proposed this be restricted to the area around Charleston, South Carolina. Campbell and Lamar (2004) mentioned this species as being found in Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Mississippi, Missouri, North Central and Eastern Nebraska, Southern New Jersey, North Carolina, Oklahoma, South Carolina, Texas, and Virginia. Maps provided by Campbell and Lamar (2004) and Wright and Wright (1957) also indicate its presence in Western and Middle Tennessee and extreme southeastern Kansas, and limit it to the western part of Kentucky. In Georgia, it is found in the southern half of the state up to a few kilometers north of the fall line with few exceptions. Its range also includes the Ohio River Valley as far north as southern Illinois, and it inhabits many barrier islands off the coasts of the states where it is found.
This is the most aquatic species of the genus Agkistrodon, and is usually associated with bodies of water, such as creeks, streams, marshes, swamps and the shores of ponds and lakes. The U.S. Navy (1991) describes it as inhabiting swamps, shallow lakes and sluggish streams, but it is usually not found in swift, deep, cool water.  Behler and King (1979) list its habitats as including lowland swamps, lakes, rivers, bayheads, sloughs, irrigation ditches, canals, rice fields and small clear rocky mountain streams. It is also found in brackish water habitats and is sometimes seen swimming in saltwater. It has been much more successful at colonizing Atlantic and Gulf coast barrier islands than the copperhead, A. contortrix. However, even on these islands, it tends to favor freshwater marshes. A study by Dunson and Freda (1985) describes it as not being particularly salt tolerant. 
The snake is not limited to aquatic habitats, however, as Gloyd and Conant (1990) mentioned large specimens have been found more than a mile (1.6 km) from water. In various locations, the species is well-adapted to less moist environments, such as palmetto thickets, pine-palmetto forest, pine woods in East Texas, pine flatwoods in Florida, eastern deciduous dune forest, dune and beach areas, riparian forest and prairies.

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The aggressiveness of these snakes has been greatly exaggerated. In tests designed to measure the various behavioral responses by wild specimens to encounters with people, 23 of 45 (51%) tried to escape, while 28 of 36 (78%) resorted to threat displays and other defensive tactics. Only when they were picked up with a mechanical hand were they likely to bite. When sufficiently stressed or threatened, this species engages in a characteristic threat display that includes vibrating its tail and throwing its head back with its mouth open to display the startling white interior, often making a loud hiss while the neck and front part of the body are pulled into an S-shaped position. Many of its common names, including "cottonmouth" and "gapper", refer to this behavior, while its habit of snapping its jaws shut when anything touches its mouth has earned it the name "trap-jaw" in some areas. Other defensive responses can include flattening the body and emitting a strong, pungent secretion from the anal glands located at the base of the tail. This musk may be ejected in thin jets if the snake is sufficiently agitated or restrained. The smell has been likened to that of a billy goat, as well as to a genus of common flood plain weeds, Pluchea, that also have a penetrating odor.
Harmless watersnakes of the genus Nerodia are often mistaken for it. These are also semiaquatic, thick-bodied snakes with large heads that can be aggressive when provoked, but they behave differently. For example, watersnakes usually flee quickly into the water, while A. piscivorus often stands its ground with its threat display. In addition, watersnakes do not vibrate their tails when excited. A. piscivorus usually holds its head at an angle of about 45° when swimming or crawling. Brown (1973) considered their heavy muscular bodies to be a striking characteristic, stating this made it difficult to hold them for venom extraction owing to their strength.
This species may be active during the day, as well as at night. However, on bright, sunny days, they are usually found coiled or stretched out somewhere in the shade. In the morning and on cool days, they can often be seen basking in the sunlight. They often emerge at sunset to warm themselves on warm ground (i.e., sidewalks, roads) and then become the very active throughout the night, when they are usually found swimming or crawling. Contrary to popular belief, they are capable of biting while underwater.
In the north, they hibernate during the winter months. Niell (1947, 1948) made observations in Georgia and noted they were one of the last species to seek shelter, often being found active until the first heavy frosts. At this point, they moved to higher ground and could be found in rotting pine stumps by tearing away the bark. These snakes could be quite active upon discovery and would then attempt burrow more deeply into the soft wood or escape to the nearest water. In southeastern Virginia, Wood (1954) reported seeing migratory behavior in late October and early November. During a period of three or four days, as many as 50 individuals could be seen swimming across Back Bay from the bayside swamps of the barrier islands to the mainland. He suggested this might have something to do with hibernating habits. In the southern parts of its range, hibernation may be short or omitted altogether.

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Raymond Ditmars (1912) described this species as "omnicarnivorous". Its diet includes mammals, birds, amphibians, fish, snakes, small turtles and small alligators. Cannibalism has also been reported. Normally, though, the bulk of its diet consists of fish and frogs. On occasion, juvenile specimens feed on invertebrates.  Catfish are often eaten, although the sharp spines sometimes cause injuries. Toads of the genus Bufo are apparently avoided. Many authors have described the prey items taken under natural circumstances. Although fish and frogs are their most common prey, they will eat almost any small vertebrate. Campbell and Lamar (2004) provided an exhaustive list of species that have reportedly been preyed upon by A. piscivorus, including cicadas, caterpillars, land snails (Euglandina rosea), catfish (Ictalurus furcatus), pike (Esox ssp.), sunfishes (Lepomis ssp.), bass (Micropterus ssp.), sirens (Siren spp.), eastern newts (Notophthalmus viridescens), brook salamanders (Eurycea spp.), Ouachita dusky salamanders (Desmognathus brimleyorum), spadefoot toads (Scaphiopus), eastern narrowmouth toads (Gastrophryne carolinensis), northern cricket frogs (Acris crepitans), West Indian treefrogs (Osteopilus septentrionalis), treefrogs (Hyla spp.), true frogs (Rana spp.), green anoles (Anolis carolinensis), skinks (Eumeces spp.), eastern glass lizards (Ophisaurus ventralis), ground skinks (Scincella lateralis), mudsnakes (Farancia abacura), hog-nosed snakes (Heterodon platirhinos), kingsnakes (Lampropeltis spp.), watersnakes (Nerodia spp.), crayfish snakes (Regina spp.), brown snakes (Storeria dekayi), gartersnakes and ribbonsnakes (Thamnophis spp.), other cottonmouths (A. piscivorus), rattlesnakes (Crotalus spp.), common snapping turtles (Chelydra serpentina), mud turtles (Kinosternon spp.), common musk turtles (Sternotherus odoratus), Florida cooters (Pseudemys floridana), sliders (Trachemys scripta), eastern box turtles (Terrapene carolina), Florida softshell turtles (Apalone ferox), baby American alligators (Alligator mississippiensis), wood thrushes (Hylocichla mustelina), chickadees (Parus spp.), cardinals (Cardinalis cardinalis), unidentified passerines, small ducks, juvenile anhingas (Anhinga anhinga), common egrets (Ardea alba), egrets, glossy ibises and their eggs (Plegadis falcinellus), tricolor herons (Egretta tricolor), herons and their eggs, pied-billed grebes (Podilymbus podiceps), short-tailed shrews (Blarina brevicauda), least shrews (Cryptotis parva), southeastern shrews (Sorex longirostris), eastern moles (Scalopus aquaticus), muskrats (Ondatra zibethicus), rice rats (Oryzomys palustris), hispid pocket mice (Perognathus hispidus), black rats (Rattus rattus), squirrels (Sciurus' spp.), rabbits (Sylvilagus spp.) and bats.
Fish are captured by cornering them in shallow water, usually against the bank or under logs. They take advantage when bodies of water begin to dry up in the summer or early fall and gorge themselves on the resulting high concentrations of fish and tadpoles. A study by Savitsky (1992) found they were surprisingly unsuccessful at seizing either live or dead fish underwater. They are opportunistic feeders and will sometimes eat carrion. Campbell and Lamar (2004) described having seen them feeding on fish heads and viscera that had been thrown into the water from a dock. Heinrich and Studenroth (1996) reported an occasion in which an individual was seen feeding on the butchered remains of a feral hog (Sus scrofa) that had been thrown into Cypress Creek. 
Conant (1929) gave a detailed account of the feeding behavior of a captive specimen from South Carolina. When prey was introduced, the snake quickly became attentive and made an attack. Frogs and small birds were seized and held until movement stopped. Larger prey was approached in a more cautious manner; a rapid strike was executed after which the snake would withdraw. In 2.5 years, the snake had accepted three species of frogs, including a large bullfrog, a spotted salamander, water snakes, garter snakes, sparrows, young rats and three species of mice. Brimley (1944) described a captive specimen that ate copperheads (A. contortrix), as well as members of its own species, keeping its fangs embedded in its victims until they had been immobilized. Young individuals have yellowish or greenish tail tips and engage in caudal luring. The tail tip is wriggled to lure prey, such as frogs and lizards, within striking distance. Wharton (1960) observed captive specimens exhibiting this behavior between 07:20 and 19:40 hours, which suggests it is a daytime activity.

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These snakes are preyed upon by snapping turtles (Chelydra serpentina), American alligators (Alligator mississippiensis), horned owls (Bubo virginianus), eagles, hawks (red-shouldered), loggerhead shrikes (Lanius ludovicianus), and large wading birds, such as herons, cranes and egrets. They are also preyed upon by ophiophagous snakes, including their own species (cannibalism). Humphreys (1881) described how a 34-inch (864 mm) specimen was killed and eaten by a 42-inch (1067 mm) captive kingsnake. 
On the other hand, Neill (1947) reported captive kingsnakes (Lampropeltis getula) were loath to attack them, being successfully repelled with "body blows".  Also called body-bridging, this is a specific defensive behavior against ophiophagous snakes, first observed in certain rattlesnake (Crotalus) species by Klauber (1927), that involves raising a section of the middle of the body above the ground to varying heights. This raised loop may then be held in this position for varying amounts of time, shifted in position, or moved towards the attacker. In the latter case, it is often flipped or thrown vigorously in the direction of the assailant. In A. piscivorus, the loop is raised laterally, with the belly facing towards the attacker.

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This species is ovoviviparous, with females giving birth to one to 16 live young and possibly as many as 20. However, litters of six to eight are the most common. Neonates are 22-35 cm in length (excluding runts), with the largest being A. p. conanti and A. p. leucostoma the smallest. If weather conditions are favorable and food is readily available, growth is rapid and females may reproduce at less than three years of age and a total length of as little as 60 cm. The young are born in August or September, while mating may occur during any of the warmer months of the year, at least in certain parts of its range. Regarding A. p. piscivorus, an early account by Stejneger (1895) described a pair in the Berlin Zoological Garden that mated on January 21, 1873, after which eight neonates were discovered in the cage on July 16 of that year. The young were each 26 cm in length and 1.5 cm thick. They shed for the first time within two weeks, after which they accepted small frogs, but not fish. 
Combat behavior between males has been reported on a number of occasions, and is very similar in form to that seen in many other viperid species. An important factor in sexual selection, it allows for the establishment and recognition of dominance as males compete for access to sexually active females.
A few accounts exist that describe females defending their newly born litters. Wharten (1960, 1966) reported several cases where females found near their young stood their ground and considered these to be examples of guarding behavior. Another case was described by Walters and Card (1996) in which a female was found at the entrance of a chamber with seven neonates crawling on or around her. When one of the young was moved a short distance from the chamber, she seemed to be agitated and faced the intruder. Eventually, all of her offspring retreated into the chamber, but the female remained at the entrance, ready to strike.

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A. piscivorus venom is more toxic than that of A. contortrix (the copperhead), and is rich with tissue-destructive enzymes. Absent an anaphylactic reaction in a bitten individual, however, the venom does not cause systemic reactions in victims and does not contain neurotoxic components that are present in numerous rattlesnake species. Bites can be effectively treated with CroFab antivenom, as this serum is derived using venom components from four species of American pitvipers (the eastern and western diamondback rattlesnakes, the Mojave rattlesnake and the cottonmouth).
Bites from the cottonmouth are relatively frequent in the lower Mississippi River Valley and along the coast of the Gulf of Mexico, although fatalities are rare. 
 Allen and Swindell (1948) compiled a record of A. piscivorus bites in the state of Florida from newspaper accounts and data from the Bureau of Vital Statistics: 1934, eight bites and three fatalities (no further fatalities were recorded after this year); 1935, 10; 1936, 16; 1937, 7; 1938, 6; 1939, 5; 1940, 3; 1941, 6; 1942, 3; 1943, 1; 1944, 3, 1998; 1. Wright and Wright (1957) report having encountered these snakes on countless occasions, often almost stepping on them, but never being bitten. In addition, they heard of no reports of any bites among 400 cypress cutters in the Okefenokee Swamp during the entire summer of 1921. These accounts indicate the species is not particularly aggressive. 
Brown (1973) gave an average venom yield (dried) of 125 mg, with a range of 80-237 mg, along with LD50 values of 4.0, 2.2, 2.7, 3.5, 2.0 mg/kg IV, 4.8, 5.1, 4.0, 5.5, 3.8, 6.8 mg/kg IP and 25.8 mg/kg SC for toxicity. Wolff and Githens (1939) described a 152 cm (60 inches) specimen that yielded 3.5 ml of venom during the first extraction and 4.0 ml five weeks later (1.094 grams of dried venom). Symptoms commonly include ecchymosis and swelling. The pain is generally more severe than bites from the copperhead (A. contortrix), but less so than those from rattlesnakes (Crotalus spp.). The formation of vesicles and bullae is less common than with rattlesnake bites, although necrosis can occur. Myokymia is sometimes reported.  On the other hand, the U.S. Navy (1991) states the venom has strong proteolytic activity that can lead to severe tissue destruction.

This species is classified as Least Concern (LC) on the IUCN Red List of Threatened Species (v3.1, 2001). Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. When last assessed in 2007, the population trend was stable. Constant persecution of the species and drainage of wetland habitat prior to development has taken a heavy toll on local populations. Despite this, it remains a common species in many areas. In Indiana, the cottonmouth is listed as an endangered species.

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[-] The following 1 user Likes Taipan's post:
  • Claudiu Constantin Nicolaescu
Ceratodromeus Wrote:Rare instance of scavenging a road-killed animal - in this case a rainbow snake:

" Herein we report a prey item
novel for A. piscivorus. On 30 April 2013 at 1147 h, one of us (AW) observed an
A. piscivorus in the process of consuming a female Farancia
erythrogramma (Rainbow Snake; SVL = 91.2 cm; total length =
104.9 cm; 1070 g) along the edge of a roadside ditch that drains
into Flint Creek, Wiggins, Stone Co., Mississippi, USA. The F.
erythrogramma appeared lifeless and had been a quarter of the
way ingested (tail first) when first detected. Upon approach the A.
piscivorus regurgitated the F. erythrogramma and fled upstream.
The head of the F. erythrograma appeared to have been crushed/
flattened and maggots (Order: Diptera) were present on the head
and first third of the body. The presence of fly larvae suggests that
the F. erythrogramma was dead prior to partial ingestion by the
A. piscivorus, and while it is unknown how the snake may have
died, a small blood stain on the adjacent road implies that the F.
erythrogramma was hit by a car. The frequency and propensity to
scavenge and the relative contribution that carrion represents in
the diet of A. piscivorus is unknown. However, carrion probably
plays an important supplementary role, as is the case with a
number of other snake species (DeVault and Krochmal 2002.
Herpetologica 58:429–436)."

Natural history notes; Herpetological review - 2014

Ceph Wrote:Comparative Study of Changes in Prey Capture Behavior of the Cottonmouth (Agkistrodon piscivorus) and Egyptian Cobra (Naja haje)
Kenneth V. Kardong
Vol. 1982, No. 2 (May 28, 1982), pp. 337-343

Prey capture behavior between cottonmouths (Agkistrodon piscivorus) and Egyptian cobras (Naja haje) differ fundamentally in response to proximate factors. Cottonmouths, when presented with several mice in close succession, tended to release the first mice but hold on to later mice. Cottonmouths, too, were more deliberate in establishing coils from which to strike than the cobra. In the Egyptian cobra, there was no appreciable change in hold/release behavior through a sequence of up to 4 mice. More important was the retaliation of the mouse when struck. Egyptian cobras usually held a struck mouse, regardless of its position in the sequence, unless bitten by the mouse. Mice which bit the cobra were usually released. Cobra struck mice died more quickly if held in the jaws and the range of death rates was less than for mice released. In both species prey size was a generally important factor influencing behavior, although more so in cottonmouths. Thus, cottonmouths and Egyptian cobras share with the Palaestinian viper (Vipera palaestinae) a tendency to change hold/release behavior in response to prey size. The site along the body where a mouse was struck affected the severity of envenomation.

[Image: ECvCM_zps2jwcdocm.jpg]

Kardong, Kenneth V. "Comparative study of changes in prey capture behavior of the cottonmouth (Agkistrodon piscivorus) and Egyptian cobra (Naja haje)." Copeia (1982): 337-343.

Ceratodromeus Wrote:Predation on rattlesnakes (From the 2014 Herpetological review)
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  • Claudiu Constantin Nicolaescu
Debunking the viper's strike: harmless snakes kill a common assumption

David A. Penning, Baxter Sawvel, Brad R. Moon
Published 15 March 2016.DOI: 10.1098/rsbl.2016.0011

To survive, organisms must avoid predation and acquire nutrients and energy. Sensory systems must correctly differentiate between potential predators and prey, and elicit behaviours that adjust distances accordingly. For snakes, strikes can serve both purposes. Vipers are thought to have the fastest strikes among snakes. However, strike performance has been measured in very few species, especially non-vipers. We measured defensive strike performance in harmless Texas ratsnakes and two species of vipers, western cottonmouths and western diamond-backed rattlesnakes, using high-speed video recordings. We show that ratsnake strike performance matches or exceeds that of vipers. In contrast with the literature over the past century, vipers do not represent the pinnacle of strike performance in snakes. Both harmless and venomous snakes can strike with very high accelerations that have two key consequences: the accelerations exceed values that can cause loss of consciousness in other animals, such as the accelerations experienced by jet pilots during extreme manoeuvres, and they make the strikes faster than the sensory and motor responses of mammalian prey and predators. Both harmless and venomous snakes can strike faster than the blink of an eye and often reach a target before it can move.

1. Introduction
For many organisms, defence and feeding involve different behaviours or different levels of performance during the same behaviour [1–4]. For many snakes, striking can be used both to catch prey and defend against predators [1,2]. Scientific descriptions of viper strikes date at least as far back as the early nineteenth century [5], and one of the first animal behaviours viewed with high-speed imagery was a rattlesnake strike [6,7]. For much of the twentieth century, the assumption that a viper strike represents ‘the fastest thing in nature’ has dominated our understanding of strike performance in snakes [5–8]. This assumption was tested with high-speed photography in 1954, which showed markedly slower strike velocities in rattlesnakes than generally expected [7]. However, the belief persists that vipers have the fastest strikes among snakes [9,10]. In order for a strike to be successful—regardless of the species involved—a snake must contact prey before it escapes or deter a threat before it causes harm. We used high-speed video recordings to test whether or not harmless ratsnakes can strike as fast as two species of vipers that often feed on similar prey and encounter similar kinds of predators.

We compared defensive strike distances, durations, and peak accelerations and velocities among species using data from 14 Texas ratsnakes (Pantherophis obsoletus; mean mass ± s.e. = 348 ± 71 g, snout–vent length = 91 ± 5.6 cm), 6 western cottonmouth vipers (Agkistrodon piscivorus; 273 ± 15.8 g, 68 ± 2.4 cm), 12 western diamond-backed rattlesnakes (Crotalus atrox; 634 ± 38 g, 95 ± 2.0 cm) and previously published studies [2,4,10,11]. We discuss the accelerations of snake strikes in relation to the known physiological effects experienced during high accelerations, and we compare strike durations with mammalian startle-response times.

2. Material and methods
We presented each snake with a target (stuffed glove) and recorded 4–8 defensive strikes per snake. We performed all trials at 27°C. To record strikes, we used a Redlake (San Diego, CA, USA) MotionScope high-speed camera set at 250 Hz and a shutter speed of less than or equal to 0.004 s. Depending on their size, we recorded snakes in an arena measuring 30 × 30 × 60 cm or 65 × 95 × 57 cm with a scale grid visible in the same plane as each snake's strike.

We analysed only strikes that were perpendicular to the camera. From the high-speed videos, we derived strike distance as the linear distance between the snake's snout and the target at the onset of the strike, and strike duration as the total time from the initiation of strike movement to first contact with the target. Maximum velocities and accelerations are the highest single (frame-to-frame) values obtained from analyses of filtered coordinates ([2]; 50 Hz cut-off Butterworth filter). We analysed peak values for each variable (often from different strikes [2]) from each snake and obtained the variables by digitizing videos using Tracker 4.87 software (Open Source Physics,

We log-transformed the data and treated strike duration (s), distance (m), maximum acceleration (ms–2) and maximum velocity (ms–1) as dependent variables. We used an ANCOVA for each dependent variable with species as the independent variable and body mass as the covariate. We also compared maximum accelerations and velocities with more complex models (one for acceleration and one for velocity) incorporating mass, species, strike distance (from the same strike that produced the maximum values) and their interactions, and subsequently excluded non-significant interactions. All model assumptions were tested and met. For maximum strike distance, two outliers were removed (standardized residual > 2) to meet assumptions. We used JMP Pro 11.0.0 and RStudio (0.99.441) for analyses, and determined significance whenever p < 0.05. We lack sufficient data for analysing muscle cross-sectional areas in these species.

3. Results and discussion
All snakes struck with very high accelerations (range = 98–279 ms–2) and velocities (2.10–3.53 ms–1), over short distances (8.6–27.0 cm), and with short durations (48–84 ms). Strike performance was not significantly different among species for three of the four variables (figure 1; table 1). Snakes displayed similar strike accelerations (F2,28 = 1.5, p > 0.23), velocities (F2,28 = 1.8, p > 0.17) and durations (F2,28 = 2.6, p > 0.09). However, peak strike distance differed significantly (F2,26 = 7.2, p < 0.01), with rattlesnakes striking shorter maximum distances than ratsnakes. The lack of corresponding differences in duration or velocity was owing to peak values coming from different and variable strikes. There was no difference among species in maximum accelerations (F2,27 = 0.91, p > 0.38) or velocities (F2,27 = 1.9, p > 0.16) in models when both mass and strike distance were included as covariates. Ratsnake strikes matched or exceeded the performance of viper strikes in other studies (table 1).

[Image: F1.medium.gif]
Figure 1.
Video images of defensive strikes by Pantherophis obsoletus (top) and Crotalus atrox (bottom) recorded at 250 frames s–1 with a Keyence camera (Itasca, IL, USA). 

[Image: Snake_Strike_speeds_zpsulvc0wuk.jpg]

Strike accelerations were similar and impressively high in all three species that we studied (table 1) and are similar to those of feeding strikes [1]. Strike accelerations are probably more important than the peak velocities [2] because strikes do not involve a chase. These accelerations have two sets of important consequences. First, the high accelerations keep the strike durations shorter than the response times of mammalian predators and prey. Mammalian startle responses can activate muscles in 14–151 ms, and produce observable movement in as little as 60–395 ms [12,13]; non-mammalian response times are not well known. Our results demonstrate that both harmless and venomous snake strikes can reach their targets in ca 50–90 ms, which is often faster than mammals can respond. These strikes are literally faster than the blink of an eye, which takes 202 ms in humans [14]. However, strike performance and prey capture in nature may not always be this high [15]. If strike durations are longer than the response times of the targets, then strike accelerations and reaches must be high enough to overcome the predator or prey once it has initiated a response. Our two highest strike accelerations (274 ms–2 from a ratsnake and 279 ms–2 from a rattlesnake) were approximately an order of magnitude greater than the jumping accelerations of black-tailed jackrabbits [16], and 30% faster than those of kangaroo rats [17,18], whose escape behaviour may have evolved in response to snake predators [18]. The impressive strike performance across species indicates that selection for rapid strike performance acts on many snakes. Snakes that defend against similar kinds of predators or feed on similar kinds of prey, such as small mammals, probably all need to have comparably high accelerations and short strike durations.

A second important consequence of strike performance involves physiological tolerances to high accelerations. Blood flow to the brain may be reduced during rapid head-first accelerations [19], such as those in snake strikes. Humans rarely experience accelerations as high as those of snake strikes. Fighter-jet pilots launching from an aircraft carrier experience take-off accelerations of only 27–49 ms–2 [20]. Without the aid of anti-gravity suits, pilots can lose consciousness at accelerations that are 21–23% of the values achieved by our snakes [19]. Even with anti-G suits, pilots lose the ability to stand up from sitting at accelerations of ca 30 ms–2 and lose the ability to move their limbs when accelerations reach 78 ms–2 [19]. Acceleration duration and heart-to-head distance are important in physiological responses to acceleration [19], as is size [21], which complicates our ability to understand how acceleration affects other animals. The long distances between the heart and head in many snakes could make them susceptible to impaired cranial blood flow during strikes, similar to the impairment that can occur during climbing [22], but the very short strike durations may preclude such physiological disruptions. The events at the end of a strike may have additional effects [19], but the effects of rapid deceleration and impact on a soft-bodied target are well tolerated by snakes.

Despite statements in the literature [9,10], vipers do not strike faster than all other snakes. Ratsnakes and vipers alike have similarly impressive strikes. Such high accelerations disrupt the physiology of other animals, but are well tolerated by the snakes and allow them to make contact before their targets can respond. Selection for high strike performance may be heavily influenced by the target's sensory and motor response capacities, which are an understudied aspect of predator–prey interactions. With so few snakes having been studied thus far, it seems likely that future research will reveal a greater range of performance in these diverse and successful predators.


1. ↵LaDuc TJ. 2002 Does a quick offense equal a quick defense? Kinematic comparisons of predatory and defensive strikes in the western diamond-backed rattlesnake (Crotalus atrox). In Biology of the vipers (eds GW Schuettt, M Hoggren, ME Douglas, HW Greene), pp. 267–278. Eagle Mountain, UT: Eagle Mountain Publishing.
2. ↵Herrel A, Huyghe K, Oković P, Lisičić D, Tadić Z. 2011 Fast and furious: effects of body size on strike performance in an arboreal viper Trimeresurus (Cryptelytrops) albolabris. J. Exp. Zool. A. 315, 22–29. (doi:10.1002/jez.645)
3. Herrel A, Gibb AC. 2006 Ontogeny of performance in vertebrates. Physiol. Biochem. Zool. 79, 1–6. (doi:10.1086/498196)CrossRefMedlineWeb of Science
4. ↵Shine R, Li-Xin S, Fitzgerald M, Kearney M. 2002 Antipredator responses of free-ranging pit vipers (Gloydius shedaoensis, Viperidae). Copeia 2002, 843–850. (doi:10.1643/0045-8511(2002)002[0843:AROFRP]2.0.CO;2)CrossRef
5. ↵Klauber LM. 1956 Rattlesnakes: their habits, life histories, and influence on mandkind. Berkeley, CA: University of California Press.
6. ↵Janoo A, Gasc J-P. 1992 High speed motion analysis of the predatory strike and fluorographic study of oesophageal deglutition in Vipera ammodytes: more than meets the eye. Amphibia–Reptilia 13, 315–325. (doi:10.1163/156853892X00021)
7. ↵Van Riper W. 1954 Measuring the speed of a rattlesnake's strike. Anim. Kingdom 57, 50–53.
8. ↵Whitaker PB, Ellis K, Shine R. 2000 The defensive strike of the Eastern Brownsnake, Pseudonaja textilis (Elapidae). Funct. Ecol. 14, 25–31. (doi:10.1046/j.1365-2435.2000.00385.x)CrossRef
9. ↵Vincent SE, Herrel A, Irschick DJ. 2005 Comparisons of aquatic versus terrestrial predatory strikes in the pitviper, Agkistrodon piscivorus. J. Exp. Zool. A. 303A, 476–488. (doi:10.1002/jez.a.179)
10. ↵Young BA. 2010 How a heavy-bodied snake strikes quickly: high-power axial musculature in the puff adder (Bitis arietans). J. Exp. Zool. A. 313, 114–11. (doi:10.1002/jez.579)
11.↵Araújo MS, Martins M. 2007 The defensive strike of five species of lanceheads of the genus Bothrops (Viperidae). Braz. J. Biol. 67, 327–332. (doi:10.1590/S1519-69842007000200019)CrossRefMedline
12. ↵Davis M. 1984 The mammalian startle response. In Neural mechanisms of startle behaviour (ed. RC Eaton), pp. 287–351. New York, NY: Plenum Press.
13. ↵Yilmaz M, Meister M. 2013 Rapid innate defensive responses of mice to looming visual stimuli. Curr. Biol. 23, 2011–2015. (doi:10.1016/j.cub.2013.08.015)CrossRefMedline
14. ↵Caffier PP, Erdmann U, Ullsperger P. 2003 Experimental evaluation of eye-blink parameters as a drowsiness measure. Eur. J. Appl. Physiol. 89, 319–325. (doi:10.1007/s00421-003-0807-5)CrossRefMedlineWeb of Science
15. ↵Clark RW, Tangco S, Barbour MA. 2012 Field video recordings reveal factors influencing predatory strike success of free-ranging rattlesnakes (Crotalus spp.). Anim. Behav. 84, 183–190. (doi:10.1016/j.anbehav.2012.04.029)CrossRefWeb of Science
16. ↵Carrier DR. 1996 Ontogenetic limits on locomotor performance. Physiol. Zool. 69, 467–488. (doi:10.1086/physzool.69.3.30164211)
17. ↵Müller UK, Kranenbarg S. 2004 Power at the tip of the tongue. Science 304, 217–219. (doi:10.1126/science.1097894)Abstract/FREE Full Text
18. ↵Biewener AA, Blickhan R. 1988 Kangaroo rat locomotion: design for elastic energy storage or acceleration? J. Exp. Biol. 140, 243–255.Abstract/FREE Full Text
19. ↵Balldin U. 2002 Acceleration effects on fighter pilots. In Medical aspects of harsh environments (eds K Pandoff, R Burr), pp. 1014–1027. Washington, DC: Department of the Army.
20. ↵Patterson D, Monti A, Brice C, Dougal R, Pettus R, Srinivas D, Dilipchandra K, Bertoncelli T. 2002 Design and simulation of an electromagnetic aircraft launch system. In Proc. 37th Industry Applications Ann. Meeting, 13–18 October 2002; Pittsburgh, PA, USA, pp. 1950–1957. Piscataway, NJ: Institute of Electrical and Electronic Engineers, Inc.
21. ↵White CR, Seymour RS. 2013 The role of gravity in the evolution of mammalian blood pressure. Evolution 68, 901–908. (doi:10.1111/evo.12298)
22. Lillywhite HB. 1987 Circulatory adaptations of snakes to gravity. Am. Zool. 27, 81–95. (doi:10.1093/icb/27.1.81)Abstract/FREE Full Text 
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  • Claudiu Constantin Nicolaescu
Viper vs. Viper! Never-Before-Seen Combat Recorded

By Mindy Weisberger, Senior Writer | September 16, 2016 02:38pm ET

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Copperheads and cottonmouths — both vipers — don't usually battle each other. Or do they?
Credit: Dennis W Donohue/Kristian Bell/

Male snakes in the viper family — a venomous group of snakes that have hinged fangs — are known for engaging in fierce wrestling matches when they compete for females. But combat between two different viper species has never been observed — until now.

On Sept. 6, Dawn Kelly was astounded to come across an unexpected and intense battle between a cottonmouth and a copperhead near her cabin in Snowball, Arkansas, close to the Buffalo National River Park in the northern part of the state.

Kelly captured video footage of the unusual encounter on her smartphone, and shared it with biologist David Steen, an assistant research professor at Auburn University Museum of Natural History in Alabama. Steen is an active science communicator on Twitter (@AlongsideWild) and on his blog, Living Alongside Wildlife. He is particularly well-known for answering questions from the public about snakes. 

In the video, two sizable males square off in a rural area next to pieces of discarded tin, wrapping their bodies around each other in a test of strength so intense that Kelly was able to film for several minutes without disturbing the serpents, she said.

Kelly told Live Science that she was in her cabin when she looked out the window and noticed that her neighbor's dog was motioning toward two snakes in the weeds. She went outside to take a closer look, and that's when she saw that not only were the snakes battling each other, but also that they were two different viper species.

Having grown up on a farm, Kelly said she was no stranger to Arkansas wildlife. She once nursed an injured king snake back to health, and described herself as "the girl who flips over every piece of plywood to see who's under it." Kelly said she was familiar with snakes in the area. Vipers like cottonmouths and copperheads are common, though they tend to be reclusive and are not seen as frequently as other types of snakes, she added. She said she recognized that what she was seeing was highly unusual, and so she started filming it with her phone.

Kelly described the vipers as "well over 2 feet [0.6 meters] long," and they were so preoccupied with each other that she was able to approach to within just a few feet of them.

"They didn't even notice me until I yelled at the dog to get away," she said.

Steen said snakes are difficult to study in a controlled manner, so a lot about how they live and interact with each other remains a mystery.

"Something like this cool behavior — you just don't see it that often," he told Live Science. "To my knowledge, no one's ever documented two different vipers in combat before."

Steen explained that the two males were likely competing for a female that was hidden from view, adding that since the vipers are different species, they typically can't interbreed. When Steen posted the footage on YouTube, he said in the description that he and other researchers would be investigating this peculiar incident further.

"It's one observation, so we don't want to read into it too much. We don't know if it's necessarily widespread behavior," Steen told Live Science. "But it does make us want to rethink what we know about how these species interact with each other." 
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  • Claudiu Constantin Nicolaescu
Stressed snakes strike first

Date: December 21, 2016
Source: Penn State

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Cottonmouth snake with mouth open showing signature white mouth.
Credit: Mark Herr/Penn State

Whether a wild cottonmouth snake will attempt to strike in an encounter depends on its baseline stress level, according to a team of scientists led by undergraduate researcher Mark Herr.

"Most people think a snake is more likely to strike after you have handled or harassed it," said Tracy Langkilde, professor and department head of biology. "Our results show this is not true. We show that how stressed a snake gets when handled or harassed does not determine how likely it is to strike."

The researchers found that cottonmouths with high baseline levels of corticosterone, a hormone that is used to estimate the amount of stress an animal experiences, were more likely to strike during an encounter with a person than were cottonmouths with lower baseline levels of corticosterone. Surprisingly, an increase in corticosterone levels that occurred after a standardized stressful experience did not make the snakes more likely to strike.

Only eleven of the thirty-two snakes in the experiment struck after being held by snake tongs on their first encounter. After a short period of stressful confinement, just seven of the snakes attempted to strike when held by tongs. These results, recently published online in the journal, General and Comparative Endocrinology, suggest that cottonmouths are not as aggressive as popular lore suggests and that the level of aggression a cottonmouth displays during an encounter may often be exaggerated.

Based on this work, the researchers suggest that protecting the habitats of snakes so they do not routinely experience high stress may be an effective way to reduce the incidence of snakebite. If snakes are not stressed, they may be less likely to strike humans when encountered. These results may have implications in the developing world where snakebites from all species result in 25,000 to 125,000 deaths a year and up to 400,000 amputations annually.

Although stress is considered an important factor affecting behavior, the interaction between stress hormones and behavior in wild animals is not well understood. This motivated the researchers to design an experiment that could gain insight into how stress drives behavior in snakes in the real world. The researchers selected the cottonmouth snake, a venomous pit viper endemic to the southeastern United States because it has a clear suite of anti-predator behaviors that are easy to measure. Anti-predator behaviors include flashing the white lining of mouth -- which gives the snake its common name -- vibrating the end of its tail, flicking its tongue, hissing, fleeing the scene and striking.

The research team included Herr, Langkilde and Sean Graham, a former post-doctoral researcher in the Langkilde lab who is now assistant professor at Sul Ross State University. Langkilde, an expert in animal behavior, Graham, an expert in stress physiology with previous experience studying cottonmouth snakes, and Herr combined their expertise to design the field experiment. Herr and Graham then set out to selected field sites in Alabama to collect data.

The team explored beaver marshes and cypress swamps in search of cottonmouth snakes to stage threatening encounters. In an encounter, Herr and Graham would stand one meter away from a snake and record any anti-predator behavior. After 15 seconds, Graham would grab the snake at mid-body with tongs and observe the snake for 15 seconds for any changes in behavior. After placing a clear plastic tube around the head of the snake to prevent it from striking, Herr would draw a blood sample from the tail. Blood samples were used to measure corticosterone levels. The snake was then placed in a 5-gallon bucket for 30 minutes to subject it to a stressful confined environment. The researchers then held the snake with tongs again, recorded its behavior, and took another blood sample to measure post-confinement corticosterone levels.

They found that confinement did raise corticosterone levels in the snakes, but that whether a given snake would strike during the subsequent encounter was not related to its post-confinement corticosterone level or to how much its corticosterone went up during the experiment. These results showed that a snake's striking behavior was related to its baseline level of corticosterone -- its level of stress before the encounter -- but not to its level of corticosterone after a short period of handling and confinement stress.

"These are some of the first results we know of that connect stress biology with anti-predator behavior in the wild," said Herr.

According to the researchers, the main limitation of this study is that the researchers only show a correlation between baseline corticosterone levels and behavior in cottonmouth snakes. In other words, the researchers did not demonstrate that high baseline stress levels cause a cottonmouth to strike. To answer this question and exclude other possible causes like genetics, they are planning an experiment to manipulate the stress levels of cottonmouths to understand the impact this factor has on snakes' behavior.

Story Source: Penn State. "Stressed snakes strike first." ScienceDaily. (accessed December 22, 2016).

Journal Reference:
Mark W. Herr, Sean P. Graham, Tracy Langkilde. Stressed snakes strike first: Hormone levels and defensive behavior in free ranging cottonmouths (Agkistrodon piscivorus). General and Comparative Endocrinology, 2017; 243: 89 DOI: 10.1016/j.ygcen.2016.11.003

Stress is believed to be an important factor mediating animal behavior. Here we explore the relationship between concentrations of a stress hormone and defensive behavior of a snake. The cottonmouth (Agkistrodon piscivorus) is an abundant, large-bodied pitviper that is well known for its intense defensive behaviors. The defensive behaviors and hormonal ecology of cottonmouths have been studied extensively, but the interaction between these is not well understood. We conducted field trials, recording the snake’s behavior and obtaining blood samples to quantify plasma CORT concentrations, both upon first encountering a snake and after a 30 min standardized confinement stressor. We found that snakes with elevated levels of baseline CORT at first encounter were more likely to strike than exhibit a threat display when approached in the field. However, this behavior was not related to the magnitude of the snake’s CORT increase following confinement, suggesting that more stress-prone snakes are not more defensive. Post-stressor antipredator behavior was also not related to any of our CORT measures. This study suggests that baseline CORT levels can be important correlates of defensive behavior. If this is a causative relationship, environmental challenges that increase baseline stress levels of populations may elevate cottonmouth defensive behavior. This would increase costs associated with defensive behavior (energetic, lost opportunity, etc.) and have important consequences for animal-human interactions. 
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  • Claudiu Constantin Nicolaescu

At 1617 h, 19 October 2016 (overcast, 26.5°C), I observed an adult Tamias striatus (Eastern Chipmunk) near the edge of a wet-land in Shawnee National Forest, Union County, Illinois, USA, where large numbers of A. piscivorus pass between active- and inactive-season habitats in spring and autumn (Palis 2015. Trans. Illinois State Acad. Sci. 108:39–42). The T. striatus was unsteady and having difficulty standing. It moved forward one body length, 
collapsed within 30 cm of the wetland edge, and stopped breathing. Suspecting envenomation by an adult A. piscivorus that I had seen 1.75 m away beneath a thicket of greenbriar (Smilax sp.), I briefly vacated the area to prevent interfering with the snake’s prey searching behavior. Upon my return at 1624 h, I found the 
A. piscivorus (total length = ca. 76 cm) swallowing the T. striatushead first (Fig. 1). To my knowledge, this is the first report of A. piscivorus consuming T. striatus.

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