In our area people who machete bushes and weeds day after day and see more snakes than anyone are absolutely convinced that nearly every snake they encounter is deadly. My experience is that in the northern Yucatan Peninsula venemous snakes are uncommon, maybe because for many generations men with machetes have been hacking away at them.
Having that said, you might want to check out my pages on the Neotropical Rattlesnake met near Chichen Itzá and the Variable Coral Snake seen on Quinta Roo's southern coast. Also, keep in mind that this page speaks of the northern Yucatan. Eastern, central and southern Yucatan are rainier, lusher, and snakier.
In arid, scrubby to somewhat scrubby, northwestern and north-central Yucatan there are four venomous snake species:
1) Neotropical Rattlesnake, CROTALUS DURISSUS
2) Cantil, AGKISTRODON BILINEATUS
3) Variable Coral Snake, MICRURUS DIASTEMA
4) Yucatan Hognose Pitviper, PORTHIDIUM YUCATANICUM
In northeastern Yucatan, and all the Yucatan's rainy eastern side, there's a fifth venomous species:
5) Barba Amarilla (Fer de Lance or Terciopelo), BOTHROPS ASPER
Farther south in much rainier, high-forest areas other venomous snakes occur: The Jumping Pitviper; the Eyelash Palm-pitviper, and; the Rainforest Hognosed Pitviper.
The vast majority of snakes with red, yellow and black bands identified as coral snakes turn out to be other species, especially the Tropical Milksnake, LAMPROPELTIS TRIANGULUM. Milksnakes are harmless but in Nature protect themselves by looking like coral snakes. You can see how similar milksnakes are to coral snakes by comparing the harmless milksnake shown on its Wikipedia page with the dangerous Variable Coral Snake on our page at http://www.backyardnature.net/yucatan/v_coral.htm
There's this saying, "Red on yellow, kills a fellow," meaning that on coral snakes the red band is fringed with narrow yellow bands -- red on yellow. However, sometimes on coral snakes the yellow bands are missing.
The thing to do in wild areas is always to watch where you put your hands and feet, and just don't fool with any snake the identity of which you're unsuref. And keep in mind that snakes nearly always are afraid of you, and want to stay away from you.