The most dangerous venomous animals of the Southwest

Speckled-rattlesnakeThe southwestern desert has a reputation for venomous critters, but which are most dangerous? I attended a lecture at the Arizona-Sonora Desert Museum given by James W. Cornett, a biologist, author, and emeritus Curator of Natural Science at the Palm Springs Desert Museum. Cornett has studied venomous animals for over 30 years and gave us a list of what he considers the thirteen most dangerous animals.

This list is subjective and includes consideration of the toxicity of the venom, the amount of venom injected, the possibility of an allergic reaction, the abundance of the animal, and the probability you could actually encounter the animal. Here is his list from the least dangerous to most dangerous:

13. Tarantulas. The venom is generally not dangerous to humans and it takes much provocation to get a tarantula to bite you.

12. Centipedes. Some of these can get over 10 inches long (but most are about 5 – to 8 inches) They deliver venom by pinching with its front legs. One death has been attributed to a centipede bite.

11. Velvet ants (actually wasps). These look fuzzy and cute but deliver a very painful bite.

10. Gila monster. These lizards are venomous but it takes some provocation to get them to bite you. (Note: that provocation can be trying to be nice and carrying one off the road so that it doesn’t get run over.)

9. Coral snakes. The coral snakes in the Southwest are generally small. More deaths occur in the East where the snakes are larger.

8. Cone-nosed bugs (aka Kissing bugs). Bites from these bugs can produce an allergic reaction and can transmit Chagas Disease, a chronic and debilitating protozoan infection. Cone-nosed bugs feed on the blood of other animals, mostly rodents.

7. Ants. Swarming ants, by their large numbers can deliver painful bites and cause allergic reactions.

6. Scorpions. Most scorpion stings in the southwest are not dangerous. However, bark scorpion venom is dangerous to humans.

5. Brown (recluse) spiders. The venom is very persistent and causes tissue damage.

4. Wasps.

3. Black Widow spiders. Drop for drop, black widow venom is the most toxic of any animal in the southwest. And now, we are seeing more Brown Widow spiders coming into the area.

2. Rattlesnakes. This venom does great tissue damage and two species, the Tiger rattlesnake and Mohave rattlesnake also have neurotoxic venom. By the way, there are 18 rattlesnake species common to Arizona.

And the most dangerous venomous animal:

1. Africanized Honey Bees. According to Cornett, bees cause more deaths than all the other animals combined.

Besides these animals, Cornett mentioned some snakes that are considered only mildly venomous, some of which are commonly kept as pets. None of these snakes have fangs, but the do have enlarged back teeth and toxic saliva. They need to chew on you for a while to work the venom in. These snakes include the ring-necked snake, black-headed snake, spotted night snake, lyre snake, hog-nosed snake, and the common garter snake.

Cornett related an incident with a hog-nosed snake. This snake was in an exhibit at the Palm Springs Desert Museum. Cornett was attempting to feed it a mouse, but since he handled the mouse, its scent got on Cornett’s hand. The snake bit him on the web between thumb and forefinger and chewed for a while before it could be detached. This mild venom caused swelling and discoloration of Cornett’s hand and arm and produced blisters for about a month. Nobody has antivenom for these snakes.

For more information on venomous animals, see:

Desert Bees and Africanized Bees

Scorpions, Vinegaroons, and Sun Spiders

Tarantula Hawks Deliver The Big Sting

Venomous Centipedes and Cyanide-Oozing Millipedes

Who’s Afraid of Tarantulas?


Venomous Lizards

Venomous Centipedes and Cyanide-Oozing Millipedes

Among the creepy-crawly critters in the Sonoran Desert are centipedes and millipedes, both of which have some interesting properties.


The Giant Desert Centipede (Scolopendra heros) can grow up to 8 inches long. The body is usually yellowish-tan, and the head and tail segments are black. The common desert centipede (Scolopendra polymorpha) is 4- to 5 inches long, and brown to tan. Centipedes have a flattened, segmented body with one pair of legs per segment. If the centipede is not moving, it can be hard to distinguish the back end from the front end because both have antenna-like appendages. But, just under the head are powerful pincers (gnathopods) which can delivery a very painful pinch and venom. The venom is not harmful to humans, but don’t try to pick up a centipede.

Centipedes are fast-moving predators that feed upon any small animal they can catch, primarily insects, but they are known to take other arthropods, lizards, and also small rodents. Centipedes usually hunt at night, but may be out in the daytime during the rainy season. Female centipedes will guard their eggs until they hatch. The centipede usually prefers slightly damp micro-habitats beneath rocks or in debris such as dead saguaros. Despite the name “centipede” Scolopendra usually have 42 legs. The number of legs depends on the species.

The Desert Millipede (Orthoporus ornatus) has a cylindrical body, up to 6 inches long. Body color varies from reddish-brown to black. Millipedes have two pairs of legs per segment. They begin life with only a few segments and add segments and legs as they grow. Millipedes are quite adaptable and occur throughout the world. They prefer humid environments and are commonly seen following summer rains (their nickname is “rainworm”).


Millipedes are nocturnal and feed on living and decaying plant material, and that includes cholla, creosote bush, ocotillo, and mesquite. They also ingest soil and help play a role in soil conditioning. For defense, it usually rolls into a coil. Upon further provocation, millipedes use chemical warfare. They can secrete, and shoot up to 10 inches, a liquid which contains benzoquinones, aldehydes, hydrocyanic acid, phenols, terpenoids, nitroethylbenzenes, and other substances. This can be very irritating. However, millipedes are usually gentle; I’ve handled them without any problem. Some people keep them as pets. Millipedes don’t bite.

Both centipedes and millipedes spend most of their time underground.