How do you tell the difference between a venomous (“poisonous”) and a non-venomous snake?
This question has no easy answer and any snake that cannot be positively identified as harmless should not be picked up. Pit vipers have large, triangular shaped heads, but so do non-venomous water snakes. Pit vipers have elliptical pupils, whereas all harmless snakes in the eastern United States have round pupils; but so do venomous coral snakes. No single rule separates all of the venomous species from all of the harmless ones, except the presence of fangs.

Do harmless snakes ever interbreed with dangerous ones?
Although there are rare examples of similar species hybridizing in the wild, no instances are known of pit vipers or coral snakes breeding with non-venomous species. Can the bite from a non-venomous snake such as a kingsnake or racer make a person sick?
The bite from these snakes is for the most part harmless. In fact, with routine cleaning with soap and water, even the chance of infection is very unlikely.

What can I put around my yard to repel snakes?
No surefire product will repel snakes from a yard, although some commercial products containing sulphur or naphthalene (mothballs) are sold with claims to do so. The amount required to be effective against snakes would make the place unlivable for most everything, including people.

Can a cottonmouth (water moccasin) bite underwater?
Yes. Cottonmouths feed on water snakes, frogs and fish, which they often catch in water.