A Key to the Lizards and Poisonous Snakes (Order Squamata) in Western Pennsylvania
By Brian
1. External limbs present; eyelids moveable; an external ear opening. Lizards, Suborder Lacertilia (Figure 1) ....................................................................................................2
1. External limbs absent; lacking moveable eyelids and external ear openings; venomous. Poisonous snakes, Suborder Serpentes (Figure 1) ......................................................9
Figure 1
2. Limbs absent, but moveable eyelids and external ear openings present; 98 or more lateral fold scales (Family Anguidae) ........................................Ophisaurus ventralis
2. Limbs present, other lizards ..............................................................................3
3. Scales small, shiny and unkeeled ........................................................................4
3. Scales strongly keeled giving a rough appearance, may not be as easily noticed on smaller species (Family Iguanidae) .........................................................................7
4. Very long tail, rough to touch; 8 rows of large rectangular scales on belly (Family Teiidae) ..........................................................................Cnemidophorus sexlineatus
4. Tail not as long relative to head-body length as members of preceding family; all scales on belly approximately the same size (Family Scincidae) ........................................5
5. One postmental scale on chin (Figure 2); four light lines running lengthwise on body; no light lines on top of head ................................................................Eumeces anthracinus
5. Two postmental scales on chin (Figure 2) ......................................................6
Figure 2
6. No postlabial scales, or one or two small ....................................Eumeces laticeps
6. Two postlabial scales, relatively large; five light lines running lengthwise on body; two light lines on head (adult males have traces of stripes only) ................Eumeces fasciatus
7. Head spines present with the two central ones much longer than any of the others; fringe scales at the sides of the abdomen .(not in PA) ............................Phrynosoma cornutum
7. No spines on the head, and no fringe scales present ..............................................8
8. Dorsal scales keeled and pointed, giving a very rough appearance; female with dark wavy lines across back; male unicolored above with blue throat patch surrounded by black ...................................................................................................Sceloporus undulatus
8. Dorsal scales weakly keeled and less pointed; coloration varies: green or brown or mottled with both (also called the New World "chameleon"); pink throat fan in males; tail round (Not in PA) .................................................................................................Anolis carolinensis
9. Shiny with red, yellow, and black rings completely encircling the body; end of snout is black, followed by a yellow band across the head; red and yellow rings touch (Family Elapidae) ............................................................................................................Micrurus fulvius
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Body Form of Elapid |
Body Form of Pit Viper |
9. Not having a pattern as colorful as preceding group; having a deep pit between the eye and the nostril, scales under the tail in only one row (Family Viperidae; Subfamily Crotalinae) .....................................................................................................................................10
10. Rattle or button present at end of tail .......................................................................11
10. No rattle or button present at end of tail; anal plate single, single row of scales under tail .....................................................................................................................................12
11. Top of head covered with nine plates (Figure 3); large rounded spots on medium to dark gray ground color ................................................................................Sistrurus catenatus
11. Top of head covered with numerous small scales (Figure 3); yellow phase; dark spots or crossbands, no head markings; black phase: black predominates ...........Crotalus horridus
Figure 3
12. Coppery-red head and hourglass pattern on body; bands wide at sides of body, narrow across back ..................................................................................Agkistrodon contortrix
12. Head Markings obscure; body coloration variable: olive, brown, or black above; belly lighter; dark crossbands evident in young and subadults; white interior to mouth ..........................................................................................................Agkistrodon piscivorus
Sources for this key include...
Smith, Hobart M., A Guide To Field Identification: Reptiles of North America. Golden Press, New York, c. 1982.
Hart Thomas, Laboratory Manual For Field Biology. Washington and Jefferson College.