How can I tell the difference between a venomous snake and a harmless one?
Unfortunately, there is no one simple hard and fast criterion a person can use to tell a venomous snake from a harmless one. None of the popular criteria such as a broad, triangular head, a heavy body, cat's eyes (vertical pupils), a flat body, or rough scales are safe since both harmless and dangerous snakes are known to share some or all of these traits. The only unfailing method is an examination of the snake hollow of grooved fangs and venom glands. For obvious reasons, this is not a practical approach. A better method is to know which venomous snakes occur in your area and have a good idea about what they look like. With this in mind, keep a copy of a good field guide to Texas snakes handy, and remember a few simple facts. While many species of harmless snakes will vibrate their tail, only rattlesnakes have rattles which produce a recognizable "cicada-like" buzz. And while most rattlers will sound their rattles when they sense your presence, this is not always the case. If you catch a rattlesnakes totally by surprise, it may choose to strike first.
Pit vipers, such as rattlesnakes, water moccasins, massasaugas, and copperheads, do have cat's eyes with vertical pupils, but so do Texas lyre snakes, Northern cat-eyed snakes and Black-lined snakes which are harmless. Knowing the range of these latter snakes and knowing where you are will make this a more valuable criterion. The Texas lyre snake occurs only in extreme West Texas while the Texas cat-eyed snake and the Black-lined snake occur in extreme South Texas.
Coral snakes, which are venomous, do not have cat-eye's. They are the only venomous snake in Texas that is brightly colored red, yellow, and black bands completely encircling the body. Because harmless Texas scarlet snakes and Louisiana and Mexican milk snakes share the red, black, yellow coloration pattern, it is important to
notice the order of the colored bands. A good memory-jogging device to learn is "Red next to black is O.K. for Jack; red next to yellow will kill a fellow." Finally, with scarlet and milk snakes, the bands do not completely encircle the body but stop at ground level, under-bellies being uniform in color.
Many large harmless snakes appear to have large triangular heads which are wide in proportion to the neck, especially when you are looking down at them, so this is really not a good criterion in the field. Additionally, many harmless snakes can make themselves look and act like pit vipers, the
Texas hognose snake is a good example. Water moccasins, also known as cottonmouths, do not have rattles, but the do have facial pits. Sometimes these are hard to see without binoculars and still maintain a safe distance. Blotched, Yellowbelly and Diamondback water snakes are often mistaken for water moccasins because they share thick trunks, dark, dimly patterned backs and sides, as well as the same aquatic habitat. Cottonmouths do exhibit rather distinctive behavior, however, that usually helps to differentiate them in the field. They are significantly less agile than water snakes and often hold their ground and gape open-mouthed in a threat posture. The open gape is cottony white, hence their common name.
Copperheads are venomous and can be prevalent in wooded suburban neighborhoods. While their venom is only about half as destructive as that of an equal quantity of western diamonback venom, they are sometimes
hard to see in habitat. Due to their cryptic coloration, they blend in beautifully with their surroundings. While they are not highly aggressive, they often get stepped on. According to Alan Tennant in
Texas Snakes, not a single death resulted from 308 copperhead bites over a 10-year period.
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http://www.tpwd.state.tx.us/learning/junior_naturalists/moresnakes.phtml#s20
