[RWebb]

I guess I don't count Mexico.

nor did I say "species"

there are:
1. Crotalus spp. (rattlesnakes; about 27 spp.)
2. Agkistrodon piscivorus (Cottonmouth) - rather aquatic, esp. brackish waters
3. Agkistrodon contortrix (Copperhead) - rel. terrestrial
4. Micrurus spp.(Coral snake) - 3 spp. IIRC

a herpetologist will want to know about species and subspecies, rasenkries and etc.

those who want to know what to avoid will work off of 4 types

I'm also not counting sea snakes...