The fossil record of snakes is poorer than that of other squamates. The oldest snake is Lapparentophis defrennei from the late Cretaceous (100 MYA) in Algeria. Several of the early fossils are assigned to extant families. There are 15 families recognized with approximately 2700 species. Many derived characters diagnose the suborder Serpentes, but few of these are restricted to the group, and many are seen in other squamates, especially limb-less or burrowing taxa (e.g. amphisbaenians, pygopodids, and skinks). Like all squamates they are diapsids. An important distinction between Lacertilia (lizards) and Serpentes is the mobility among the bony elements of the skull. The skull is more specialized than most lizards in that the jaw is loosely joined together and to the cranium. The mandibles are connected by cartilage. In general, snakes have three-dimensional movement of the skull bones; however, in lizards it is limited to two-dimensional movement. In other words, skull bones of lizards are not able to move laterally. This influences the types of feeding behavior; snakes are able to consume much larger prey items (up to several times larger than their own heads). Snakes use their forked tongues to pick up scent molecules from the air and process that information in the Jackobson's organ (openings of which are located in the roof of the mouth). Snakes are found in marine, aquatic, terrestrial and arboreal habitats and are found on every continent except Antarctica. There are venomous and non-venomous varieties, with the largest concentration of venomous snakes occurring in Australia. The boids, which are non-venomous, include the largest snake in the world (Eunectes murinas). All oviparous snakes, (including even sea snakes) must lay their eggs on land.
Serpentes is divided into two major groups, Scolecophidia and Alethinophidia. Several characters of the eye, skull structure, and soft anatomy support the monophyly of Scolecophidia, the blind snakes. Alethinophidia is a much more diverse group and contains the remaining families of snakes. Characters of the skull, nervous system, and axial muscles support Alethinophidia. Relationships among families of Alethinophidia are still being investigated. More information can be found in Wright and Wright's Handbook of Snakes of the United States and Canada.
Goals: In this lab we will examine the diversity of the snakes through the use of preserved material. You are to use the dichotomous key provided to help guide you through identification. It is imperative to use this key so you can focus on the characteristics that diagnose the different species, genera and families, you will be responsible for knowing these diagnostic characters.
You are responsible for being able to identify any of the lab specimens on an exam. You are required to know all Illinois specimens to the species level; non-Illinois, U.S. specimens to the genus level; and non-U.S. specimens to the family level. Full credit on exams is given only for the proper scientific name; use of the common name on exams will be worth only half credit. Further, you should know the distribution of the Illinois species within the state, the genera within the U.S., and the families in the world. Please note as before that preservation in ethanol will eventually remove the natural colors from a specimen. The colors indicated below may therefore not be present in some specimens.
ORDER SQUAMATA
As mentioned in the lizard lab, the order Squamata is a monophyletic group that includes lizards and snakes. Investigations into the higher level relationships of squamates reveals that the suborder Lacertilia (lizards) is a paraphyletic group because snakes (the suborder Serpentes) is derived from within lizards.
Suborder "Serpentes"
Scolecophidia (Blind Snakes)
All scolecophidians have blunt heads, short, blunt tails (often tipped with a spine), smooth scales, and lack enlarged ventral scales. Eyes are vestigial and lie beneath large head scales. All are fossorial and usually associate with termite and ant nests where snakes feed on soft-bodied termites and larval ants. Scolecophidians are comprised of three families, Anomalepididae, Leptotyphlopidae and Typhlopidae. No good external characters exist to distinguish between the three families, so will need to know only one, the North American family Leptotyphlopidae.
Family Leptotyphlopidae
This is the only scolecophidian family that has teeth. See description under Scolecophidia. There are 2 genera and approximately 80 species.
Distribution - southwestern U.S. to northern South America, Africa and the Middle East
Leptotyphlops - Slender Blind Snakes
Diagnosis
Species in Leptotyphlops are found in loose soil associated with damp subsoil. Moist soil conditions must be met because Leptotyphlops are susceptible to drying. Like other scolecophidians, the genus feeds almost exclusively on ant eggs, larvae and pupae, and termites. Occasionally these snakes emerge on the surface on at night or on overcast days.
Distribution - southwestern U.S. and Mexico
Alethinophidia - "all other snakes"
Characters of the skull, nervous system and axial musculature support the grouping Alethinophidia.
Family Aniliidae
The family Aniliidae consists of a single viviparous species, Anilius scytale. It possesses bright red and black bands, a reduction in ventral scale size, and tightly fused skull, typical of fossorial snakes. Like other fossorial taxa, its eyes are vestigial and lie beneath a large head shield. Vestigial pelvic girdle and hind limbs present. Anilius is associated with tropical rain forests, where it feeds on caecilians and amphisbaenians.
Distribution - South America
Family Boidae (Boas and Pythons)
There are 20 genera and approximately 63 species. A diverse family, the Boidae includes pythons, boas, and sand boas. Generally, boids are heavy-bodied snakes with vertical pupils and smooth, glossy scales. Vestigial hind limbs are present, and may be seen externally. Males tend to have a small spur on each side of the vent. Boids are terrestrial, arboreal, aquatic, and semi-fossorial, and occur in a wide variety of environments including rain forests, dry tropical forests, mountain cloud forests, deserts, and temperate coniferous forests. Specialized infrared-sensitive pits are usually present in the upper or lower labial scales, but are variable in presence (absent in sand boas), position (sometimes in the rostral scales), and number. As the name Boa constrictor suggest, boids constrict their prey. Pythons are found primarily in the Old World and are oviparous. Boas are found in both the New and Old World and are viviparous.
Distribution - western North American through South America, West Indies, Solomon Islands, Madagascar, southern Africa, southern Asia, Indoaustralian Archipelago, Australia
Charina - Rubber Boa
Diagnosis
The rubber boa is a stout-bodied snake that has the appearance of rubber. Distinctive folds of the skin can been seen when the body is bent on acute angles (please do not bend the snake). Charina is semi-fossorial and nocturnal, sharing habits with its prey, small rodents and shrews. When feeding on rodent nests, the rubber boa defends itself from the mother by pushing her with its blunt tail. When disturbed, the snake coils into a ball to protect its head, while the tail is elevated to take the blows. Both males and females have anal spurs.
Distribution - California and Pacific Northwest
Family Colubridae
Members of the family Colubridae do not share unique derived characters, suggesting the family probably is paraphyletic. Approximately 70 percent of all snake species belong to Colubridae. There are 320 genera and approximately 1700 species. The family is further subdivided into six infrafamilial groups, which again, may or may not be monophyletic, and whose relationships are uncertain. Members of this family display reproductive modes, life histories, and habitats encompassing those seen in Alethinophidia. The family also contains several African and Asian species that are extremely venomous. These venomous species, including the African boomslang (Dispholidus), have enlarged and grooved teeth posterior on the maxilla. This condition is called "rear-fanged." Colubrids have a worldwide distribution, but have the highest diversity in North American, Europe and tropical Asia.
Specimens of the family Colubridae include South American arboreal species (long, compressed body, large eyes), fossorial North American species (small body size, reduced head width, scale reductions, inferior mouth, small eyes), and the "typical" colubrid body plan, Coluber constrictor.
Distribution - North, Central and South America, Africa, Europe, Asia, Australia
Carphophis amoenus - Midwest Worm Snake
Diagnosis
A small, fossorial species, C. amoenus prefers moist soil. During early spring, it is found under rocks and logs, but as the ground becomes dry in summer, the snake takes shelter further underground. C. amoenus has a hard, slick body that is difficult to pick up, and when captured, will writhe and poke with its tail tip. The species feeds on earthworms and soft-bodied arthropods.
Illinois distribution - southern third of the state
Clonophis kirtlandi - Kirtland's Water Snake
Diagnosis
Kirtland's water snake is semi-aquatic. It occurs in wet meadows and swamp-forest habitats, but can also be found in deserted lots and parks of urban areas. Like other species of garter, brown and water snakes, Clonophis flattens its body and remains immobile when alarmed. Earthworms and slugs make up the bulk of its diet. This snake species was named after Jared P. Kirtland, an early Ohio physician and naturalist.
Illinois distribution - east-central Illinois
Coluber constrictor - Eastern Yellow-bellied Racer or Blue Racer
Diagnosis
Because racers are diurnal, and actively search for prey, humans often encounter them. Even so, the species is swift and agile, making it difficult to capture, unless caught unaware. Males are territorial during mating season, and have been reported to "chase" intruders. Racers are generalists, preying on arthropods, amphibians, reptiles (sometimes small turtles), birds, and mammals.
Illinois distribution - statewide
Diadophis punctatus - Ringneck Snake
Diagnosis
Ringneck snakes are secretive and chiefly nocturnal snakes, occurring in mesic forest. Diadophis feeds on small salamander species, including E. cirrigera, P. glutinous and Desmognathus species, and earthworms. Females are oviparous, laying 2 to 6 eggs in an adherent cluster. Defensive postures of the species includes a foul-smelling secretion and curling the tail in a corkscrew fashion to display the bright red color on the underside.
Illinois distribution - in forested areas along rivers in the Mississippi, Illinois and Wabash drainages
Elaphe guttata - Great Plains Rat Snake
Diagnosis
The great plains rat snake has climbing ability, but prefers a more terrestrial existence. It feeds on birds and mammals, which it kills by constriction. When encountered individuals will vibrate there tails and strike.
Illinois distribution - along Mississippi River in south central Illinois
Elaphe obsoleta - Black Rat Snake
Diagnosis
Black rat snakes are excellent climbers and have been found in trees and bridge supports. In the fall, black rat snakes congregate in rock outcrops to hibernate. When disturbed, this snake will vibrate its tail and strike at the offender. Rat snakes feed on birds and mammals and use constriction to subdue their prey. P. W. Smith reports finding E. obsoleta eggs in rotting wood in late summer.
Illinois distribution - absent from the northern 1/3 of the state
Elaphe vulpina - Fox Snake
Diagnosis
In life this species is the most attractive and docile of the Elaphe species which occur in Illinois. Like other species in Elaphe, E. vulpina feeds on birds and mammals and uses constriction.
Illinois distribution - northern half of the state
Farancia abacura - Mud Snake
Diagnosis
Farancia abacura is a secretive, aquatic snake inhabiting quiet ponds, swamps, and sloughs with abundant vegetation and submerged logs. The species is frequently found on roads during rainy periods. The principal diet of the mud snake consists of Amphiuma and Siren species. Females are oviparous, and remain with their eggs during incubation.
Illinois distribution - southern tip of Illinois (Shawnee Hills region)
Heterodon nasicus - Western Hognose
Diagnosis
Similar in appearance and habit, the western hognose is a slower moving animal. Most of its time is spent prowling sand prairies in search of bufonid prey. It creates small craters in the sand where it dug up resting toads. Unlike many snakes, H. nasicus is rarely found underneath objects. Instead, the species utilizes mammal runs where is remains in cold or wet weather. Like H. platirhinos, the western hognose feigns death.
Illinois distribution - prairie relicts in northwestern Illinois
Heterodon platirhinos - Eastern Hognose
Diagnosis
The eastern hognose a medium-sized, stout bodied snake. Dorsum pattern ranges from uniform gray or black to blotch pattern. This species is common in open areas where sand or porous loams are the principal soils. H. platirhinos is a semi-fossorial and appears to be strictly diurnal. Prey items are primarily toads of the genus Bufo, but other amphibians and small mammals will be taken. H. platirhinos is perhaps best know for its defense behavior. When first captured, the individual will flatten its head and anterior body. If the threat persists, the snake will then "play dead," which includes an elaborate display of death throws and voiding of bowls.
Illinois distribution - state wide
Lampropeltis calligaster - Prairie Kingsnake
Diagnosis
Prairie kingsnakes show a preference for old fields. This species is among the first snakes to emerge from hibernaculum in March, and have been seen active in December and February. L. calligaster feeds mainly on mammals; however, birds, amphibians, and reptiles are also utilized.
Illinois distribution - absent from the northern 1/3 of the state
Lampropeltis getula - Speckled Kingsnake
Diagnosis
L. getula is usually encountered under logs and flat rocks, in wooded hilly habitats. Speckled kingsnakes are constrictors and feed on other snakes, birds and mammals.
Illinois distribution - southern Illinois
Lampropeltis triangulum - Eastern Milk Snake
Diagnosis
L. triangulaum is a forest species; however in Illinois it is also found in non-wooded habitats. It is usually found by turning over logs and flat rocks.
Illinois distribution - statewide
Masticophis flagellum - Eastern Coachwhip
Diagnosis
Coachwhips are diurnal, extremely active, and one of the fastest snakes in the state. Primarily terrestrial, the snake will quickly take shelter in low branches if being pursued. Because of the speed and agility, coachwhips are very difficult to catch. When handled these snakes thrash violently and bite. Their diet consists of insects, lizards, other snakes, birds and their eggs, and mammals.
Illinois distribution - extreme southwestern Illinois
Nerodia cyclopion - Green Water Snake
Diagnosis
A large, heavy-bodied water snake, with little color pattern makes this species easy to distinguish from other Nerodia in Illinois. The species is found in slow moving water, such as lakes and swamps. Because Illinois is the northern-most part of its range, the relative abundance of the green water snake is low in our state.
Illinois distribution - extreme southern Illinois
Nerodia erythrogaster - Redbelly Water Snake
Diagnosis
Nerodia erythrogaster is one of Illinois' the largest water snakes. It occurs in quiet, slow moving waters of ponds, lakes, and swamps. Color patterns in the species are geographically variable, and help diagnose two subspecies found in Illinois. Cornered individuals strike viciously, and like other Nerodia species, excrete foul-smelling material on the handler. The diet consists of fish, including catfish, frogs, and crayfish.
Illinois distribution - southern third of the state, north up along the Illinois River
Nerodia fasciata - Banded Water Snake
Diagnosis
The banded water snake is very similar in habit to other water snakes, especially N. sipedon. The diet consists of amphibians and fish. This species has been recorded eating road killed tree frog and ranids. N. fasciata tends to be nocturnal, especially during the summer months.
Illinois distribution - extreme southern Illinois
Nerodia rhombifer - Diamondback Water Snake
Diagnosis
The diamondback water snake is common in water bodies along the Mississippi-Ohio river flood plains. It thrives in these shallow waters, even though water temperatures are extremely high in the summer. Dietary habits are similar to other water snakes.
Illinois distribution - southern third of the state, north along the Mississippi and Illinois rivers
Nerodia sipedon - Northern Water Snake
Diagnosis
Providing it is relatively free from pollution, almost any aquatic environment will be inhabited by the northern water snake. Unlike other Nerodia, this species is essentially a stream dweller, but is also be found in lakes, ponds, and swamps. The snake is easily captured when overturning rocks along the edge of water.
Illinois distribution - statewide
Opheodrys aestivus - Rough Green Snake
Diagnosis
distinct neck, large head for arboreal habitat
Opheodrys aestivus is arboreal occupying forested places and along margin habitats. Most often, these snakes are captured while crossing roads and trails, being much more conspicuous in the open. Diet includes arachnids, lepidopterans, beetles and occasionally frogs. O. aestivus are prey to many other snake species.
Illinois distribution - southern half of state
Opheodrys vernalis - Western Smooth Green Snake
Diagnosis
Opheodrys vernalis is terrestrial species, occasionally found in low bushes and in grass. It prefers prairie habitat, which explains the spotty distribution in the state. (As the prairie of Illinois is "developed," the range of this snake species decreases.) The western smooth green snake preys on soft-bodied arthropods.
Illinois distribution - northern half of state
Pituophis catenifer &endash; Bullsnake
Diagnosis
The large bullsnake is terrestrial, but will climb and burrow in search of food. Prey items are killed by constriction, and include mammals, birds, and bird eggs. The snake is common in sand prairie regions of the central part of the state. Oviparous females lay adherent clutches of 12 eggs. When encountered, the snake rapidly vibrates its tail and hisses loudly. The taxonomic status of bullsnake populations in Illinois are dynamic. Recently, the subspecific name, P. melanoleucus catenifer was elevated to specific level (P. catenifer); however this designation is still being debated. For this class, you just need to know P. catenifer, but be aware of how names change over time.
Illinois distribution - sand regions in central Illinois
Regina grahamii - Crayfish Snake
Diagnosis
R. grahamii inhabits lakes, river bottom sloughs, and prairie marshes. They feed primarily on newly molted crayfishes; however, amphibians and fish also constitute the diet.
Illinois distribution - statewide
Storeria dekayi - Midland Brown Snake
Diagnosis
The midland brown snake is found in both forested and prairie habitats, and on floodplains and uplands. It is also commonly seen in urban areas with lots of cover (i.e. trash laying around). This snake also congregates along highway shoulders, where they presumably hibernate. Females are viviparous, giving birth up to 15 individuals. Diet consists of slugs, earthworms, and the occasional newly transformed toad.
Illinois distribution - statewide
Tantilla gracilis - Northern Flat-headed Snake
Diagnosis
The smallest snake in the state, T. gracilis is strictly fossorial. Specimens can be found by overturning flat rocks found at rock slides on sandy soil. Females are oviparous. T. gracilis possess minute poison glands and rear fangs. Prey items include worms, soft-bodied arthropods and their larvae.
Illinois distribution - arid Mississippi River bluffs along southern Illinois
Thamnophis proximus - Western Ribbon Snake
Diagnosis
The western ribbon snake is semi-aquatic, and it is rarely found away from permanent water sources. When this slender and agile snake is encountered, it quickly seeks shelter. Like other Thamnophis, when captured the ribbon snake secretes and smears musk and feces on its captor. Snakes feed on frogs and fish.
Illinois distribution - western border and isolated populations in northern half of the state
Thamnophis radix - Eastern Plains Garter Snake
Diagnosis
Thamnophis radix is a species of the Great Plains. The post-glacial "prairie peninsula" allowed the species' range to be extended into the midwest region post-Pleistocene. Wet prairie areas of the northern part of Illinois is the snake's typical habitat; however it is also found in heavily cultivated regions of the state. The diet of this snake is typical of Thamnophis species (see T. sirtalis account).
Illinois distribution - northern half of the state
Thamnophis sirtalis - Eastern Garter Snake
Diagnosis
Thamnophis sirtalis is a widespread and locally abundant snake. It occurs in almost all habitats, except for the extremely dry. When first caught, T. sirtalis expels a musk from the anal glands and attempts to bite. Its diet includes amphibians, especially salamanders, earthworms, slugs, and fish. Females are viviparous, having up to 100 neonates in a litter (average is 30).
Illinois distribution - statewide
Virginia valeriae - Western Earth Snake
Diagnosis
Virginia valeriae is another fossorial snake occurring in wooded habitats. It is often found under surface objects, including forest floor debris ("it's a litter-critter"). Females are viviparous, giving birth to 2 to 9 neonates. Prey items include earth worms, soft-bodied arthropods, and snails.
Illinois distribution - southern third of the state
Family Elapidae
Elapidae is a large family containing 62 genera and approximately 280 species, including some of the world's most venomous serpents (cobras, mambas, coral snakes, and kraits). All elapids are venomous and are characterized by proterglyph dentition (single, erect, hollow fang on the anterior end of the maxilla) and a longer, less mobile maxilla then that of vipers. While the venom toxins of vipers are usually hemolytic and cytolytic, damaging blood vessels and somatic tissue, elapid venom is neurotoxic, attacking involuntary actions of the autonomic nervous system, such as swallowing, blood flow, and breathing (this is why elapids are more deadly than vipers). Scalation is similar to that of colubrids; scales generally are not keeled, as seen in vipers, and elapids lack the loreal scale. Most elapids are very small, although they do contain the longest venomous snake, the king cobra. Elapids are terrestrial, arboreal, and aquatic. Typically, terrestrial elapids are oviparous. The 70 species of marine snakes (subfamily Hydrophiinae) are viviparous, giving aquatic birth. These snakes have several morphological specializations, including a salt gland surrounding the tongue sheath, compressed body, and a fin-like tail.
Distribution - worldwide
Micrurus - Coral Snake
Diagnosis
Coral snakes occur in dry habitats of the southeastern and southwestern U.S. They are secretive, spending most time underground. The diet primarily consists of reptiles, including blind and ground snakes. Although coral snakes seldom bite, their venom is highly dangerous (see above account). Snakes should not be handled!
Distribution - southeastern and southwestern U.S.
Family Loxocemidae
Another monotypic family, Loxocemus bicolor is a Central American snake that is partially fossorial. Its snout is somewhat pointed. Rostral scale is upturned. Little is known about its natural history. Loxocemus preys on mammals and reptile eggs, including sea turtles.
Distribution - Central America
Family Viperidae
There are 20-27 genera and approximately 215 species. Vipers are the hinged-fanged, venomous snakes. They are easily recognized by the broad, triangular shaped head that is distinctly wider than the neck, vertically elliptical pupil, and a single ventral scale row posterior to the vent. Most are heavily bodied, with short tails and strongly keeled scales. Vipers may be terrestrial or arboreal, and are found in environments ranging from rain forests to deserts and mountains. The subfamily Crotalinae, which includes all of our North American species, is characterized by the unique loreal pit-organ on each side of the head. All Illinois members of the subfamily Crotalinae are viviparous.
Distribution - all continents except Australia
Please compare the two Agkistrodon species (of the family Viperidae) with the Nerodia specimens (North American water-snakes of the family Colubridae). Note the pupil shape, anal plate, and presence of pit organs in the two families.
Agkistrodon piscivorus - Western Cottonmouth, Water Moccasin
Diagnosis
Cottonmouths are most common in swamps and sloughs along rivers. Color patterns are highly variable in this species, corresponding to the four life stages of the snake. Neonates have bright chestnut dorsal patterns and a yellow tail tip (look for juveniles specimens with the yellow tail). The adult form obscures color pattern obscured by dark browns and blacks. As its name suggests, A. piscivorus primarily feeds on fish, but will take amphibians, mammals, birds and invertebrates. The cottonmouth is both diurnal and nocturnal, foraging at night mostly during hot weather. When approached, the cottonmouth will coil, gape its white-lined mouth, and vibrate its tail. Further provocation will result in striking behavior. Bites may result in serious secondary infection (complications may cause the loss of digits or hands/feet) or can be fatal.
Illinois distribution - extreme southern Illinois
Agkistrodon contortrix - Copperhead
Diagnosis
The copperhead is most commonly found in floodplain and upland woods, adjacent to rocky hillsides where hibernacula are located. This species is gregarious, and small groups occur under cover or basking among rocks. Like juvenile A. piscivorus, neonatal copperheads have sulfur-yellow tails, which darken as the snake reaches adulthood. Although copperheads tend not to be as aggressive as cottonmouths, and bites are usually not fatal to adults, caution should be used around individuals.
Illinois distribution - southern third of the state
Crotalus horridus - Timber Rattlesnake
Diagnosis
This large rattlesnake occurs in forested bluffs and rock outcrops, or abandoned buildings that attract rodents. Although it is not considered an aggressive species, the timber rattlesnake, when disturbed, will rattle its tail and prepare to strike. The bite of this species is serious, and has caused human fatalities in Illinois. In the fall, C. horridus congregates with conspecifics and Agkistrodon species at den sites, usually rock bluffs with deep fissures, to over-winter.
Illinois distribution - rock outcrops along Mississippi and Illinois rivers, southern half and un-glaciated northwestern corner of the state.
Sistrurus catenatus - Eastern Massasauga
Diagnosis
29 to 40 middorsal, light-edged, dark blotches
This small rattlesnake occurs in prairie marshes and old fields with grass cover. The majority of specimens encountered are basking on grass/sedge hammocks or crossing roads. Massasaugas take shelter in crayfish chimneys, which are a good indicator for suitable habitat. Sistrurus preys upon small mammals, birds, and amphibians. Few people have been bitten by S. catenatus in Illinois.
Illinois distribution - Isolated populations statewide, excluding extreme southern Illinois.
Family Xenopeltidae
Xenopeltidae consists of a nocturnal, burrowing snake, Xenopeltis unicolor, which inhabits rain forests. Dorsal scales are darkly colored and iridescent (in live specimens). Dorsum and head scales contrast with a broad ring around the neck and cheek. Head scales are large plates, much like colubrids, which is unusual for a snake that is thought to be primitive. Xenopeltis is anatomically similar to Aniliidae, including a tightly knit skull, but lacks a pelvic girdle and possesses moderately enlarged ventral scales. Its diet includes frogs, reptiles and small mammals. The reproductive mode of this species is unknown.
Distribution - southeastern Asia