Mexico has 460-odd snake species, the vast majority shy and nonpoisonous; they will generally get out of your way if you give plenty of warning. In Mexico, as everywhere, poisonous snakes have been largely eradicated in city and tourist areas. In brush or jungle areas, carry a stick or a machete and beat the bushes ahead of you while watching where you put your feet. When hiking or rock-climbing in the country, don’t put your hand in niches you can’t see.
You might even see a snake underwater while swimming offshore at an isolated Bay of Banderas beach. The yellow-bellied sea snake (Pelamis platurus) grows to about two feet (0.6 m) and, although rare and shy, can inflict fatal bites. If you see a yellow-and-black snake underwater, get away, pronto. (Some eels, which resemble snakes but have gills like fish and inhabit rocky crevices, can inflict nonpoisonous bites and should also be avoided.)
The Mexican land counterpart of the Pelamis platurus is the coral snake (coralillo), which occurs as about two dozen species, all with multicolored bright bands that always include red. Although relatively rare, small, and shy, coral snakes occasionally inflict serious, sometimes fatal, bites.
More aggressive and generally more dangerous is the Mexican rattlesnake (cascabel) and its viper relative, the fer-de-lance (Bothrops atrox). About the same in size (to 6 ft/2 m) and appearance as the rattlesnake, the fer-de-lance is known by various local names, such as nauyaca, cuatro narices, palanca, and barba amarilla. It is potentially more hazardous than the rattlesnake because it lacks a warning rattle.
The Gila monster (confined in Mexico to northern Sonora) and its southern tropical relative, the yellow-spotted black escorpión (Heloderma horridum), are the world’s only poisonous lizards. Despite its beaded skin and menacing, fleshy appearance, the escorpión bites only when severely provoked; and, even then, its venom is rarely, if ever, fatal.
The crocodile (cocodrilo or caimán), once prized for its meat and hide, came close to vanishing in Mexican Pacific lagoons until the government took steps to ensure its survival; it’s now officially protected. A few isolated breeding populations live on in the wild, while government and private hatcheries (for example, in San Blas ) are breeding more for the eventual repopulation of lagoons where crocodiles once were common.
Two crocodile species occur in the Puerto Vallarta  region. The true crocodile Crocodilus acutus has a narrower snout than its local cousin, Caiman crocodilus fuscus, a type of alligator (lagarto). Although past individuals have been recorded at up to 15 feet (4.5 m) long (see the stuffed specimen upstairs at the Tepic  anthropology and history museum, or in the Hotel Bucanero lobby in San Blas), wild native crocodiles are usually young and two feet (0.6 m) or less in length.
The story of Mexican sea turtles is similar to that of crocodiles: They once swarmed ashore on Puerto Vallarta  regional beaches to lay their eggs. Prized for their meat, eggs, hide, and shell, the turtle population was severely devastated. The good news is that, now officially protected, Mexican sea turtle numbers are beginning to recover their nesting numbers in some locations.
Of the four locally occurring species, the endangered olive ridley turtle (Lepidochelys olivacea), or golfina, is by far the most common. The smallest and among the most widespread of the world’s sea turtles, golfinas flock ashore at a number of Puerto Vallarta region beaches, notably Playa San Francisco  on the Nayarit Coast, and Playa Mismaloya, near La Cruz de Loreto, on the southern Jalisco Coast. At these and many other Mexican Pacific locations, determined groups of volunteers camp out on isolated beaches during the summer and fall in order to save and incubate turtle eggs, for the final reward of watching the safe return of hundreds, and hopefully someday thousands, of turtle hatchlings to the sea.
Also present in some numbers along the Puerto Vallarta regional coastline is the green turtle (Chelonia mydas), or tortuga negra (black turtle) as it’s known in Mexico. From tour boats, green turtles can sometimes be seen grazing on sea grass offshore in the Bay of Banderas.