Creatures of the Monsoon

This summer, southern Arizona – like much of the Southwest — experienced what weather mavens call a "meteorological singularity," a weather event that happens every year around the same time. The phenomenon is the Arizona monsoon, a seasonal shifting of winds that moves moisture northward from the Pacific and Gulf of Mexico in July, August, and September. The wet, wayfaring winds hit Arizona's mountains and shoot upward toward the heavens where they cool and cloud castle into thunderstorms that produce week-long bursts of rain. It's then, when temperatures drop and the air freshens with the damp scent of desert sage, that Arizona hosts a pluvial parade of animal curiosities: lizards, snakes, toads, arachnids, beetles, emerging from underground lairs, arboreal dens and grass-girdled egg cases to eat, hunt, cruise for mates, socialize, and add to the monsoon's eldritch symphony with their chorus of croaks and chirps.

There are many reasons for this riot of activity, says Carl Olson, Associate Curator for the University of Arizona's entomology department. "All animals have evolved to be active in certain windows, some by day, some by night, some at dusk," and some during monsoon season. This is partly because the monsoon moderates climate extremes, Olson says, “making hot temps more tolerable because of increased humidity." Plus, it ‘s “the real season of plant growth, so more food is available to pick and choose from." And with the plants come the plant-eaters and, in turn, the eaters of the plant-eaters. It's all part of the "magic of monsoon season," Olson says.

Arizona ranks 3^rd in the country for biodiversity and boasts one of the nation's most diverse invertebrate assemblages. "We have at least 40 species of scorpions, quite a few species of centipedes, spiders, wasps, and bees, and ants by the bushel load." That wealth attracts hoards of scientists, collectors, and poachers who wait and watch for the winds to shift and then descend upon the monsoon's cavalcade of creatures for scientific, commercial, and -- in the case of the entheogen-producing Sonoran Desert toad (Bufo alvarius) -- recreational, ends (Entheogens are psychoactive substances smoked for their “spiritual” and hallucinatory effects).

For most people, though, the monsoon season is that weird time of year when more likely than not, they will see some of Arizona's most remarkable creatures, many of which are nocturnal or spend most of the year below ground.

Monsoon Rains Bring Out Gila Monsters: MyFoxPHOENIX.com

Gila monsters, Arizona's lumbering, Halloween-colored lizards, are some of the most noticeable players. They emerge from desert burrows to drink from and bathe in rain pools, and often wander into people's yards and gardens. When the monsoonal chill becomes too much to bear, Gilas hole up in sheds and garages (see video). Marc Hammond, co-owner of Animal Experts Inc., a Tucson-based company that specializes in capturing and re-locating unwanted animal houseguests, says Gila-related calls always peak with the monsoon.

Gilas, which prey on rodents, bird eggs, and insects, can whip their necks around with rattlesnake speed and their venom is nearly as potent. What's more, Gilas are loathe to let go of something onto which they've latched, preferring, instead, to gnaw for a bit so their grooved teeth can channel venom into the wound. But Gila encounters rarely degenerate to the point where a person, and the obstinate Gila attached to them, end up in the hospital: "It's almost impossible to get accidentally bitten by a Gila monster," Hammond says. "You would have to provoke it or put your hand in its burrow." Curious pets and kids, who don't know to keep their distance, are the most common Gila-bite victims. If, for some reason, you do get bitten, says Hammond, the best way to remove the lizard is to submerge it in water or cover its nose with an ammonia-soaked rag until it lets go.

Because Gilas are a protected in Arizona, and are ecosystem specialists, living and feeding in very specific areas, animal control experts rarely relocate them to new areas, preferring, instead, to sweep them just off the property. Gilas "are an important part of the ecosystem," Hammond says, "so we don't like to move them far because we don't know what will happen to them" in a place with which they are unfamiliar.

Another common monsoon creature is the giant vinegaroon (Mastigoproctus giganteus), a species of whip scorpion. Vinegaroons are large, nocturnal arachnids that look like a mad scientist's mix between scorpion and spider. Despite their wonderfully monstrous appearance, these creatures are harmless to humans, lacking both venom and stinger. However, when threatened, vinegaroons can emit a concentrated spray of acetic acid (vinegar), hence their name. Like all arachnids, vinegaroons have eight legs, but they only use the back six to walk. The first two legs are modified to act as feelers, and the whip-like tail is actually a sensory organ.

Vinegaroons are “classic first monsoon animals,” says Dr. Justin Schmidt, an entomologist with the University of Arizona. The adults hunker in an underground cell and wait for the first rains to fall.  Once they do, the vinegaroons crawl to the surface and into the night to hunt bark scorpions and cockroaches. They are active “on any night that has high humidity,” Schmidt says, “and will stay active the entire season unless they eat their fill and can store no more fat and protein in their now corpulent bodies,” at which point they return to their burrows until the following summer.

Other fascinating monsoon critters include blister beetles and Couch's spadefoot toad (Scaphiopus couchi). Blister beetles are stout-bodied, often black or metallic-hued insects with a medieval-style arsenal: when squeezed or attacked, the beetles secrete a liquid loaded with cantharidin, a skin-blistering agent. Beetles from the genus Epicauta are monsoon regulars. The adults spend the season feeding on foliage while the predatory larvae seek out grasshopper eggs, their baby-food of choice.

Couch's spadefoot toads spend most of their lives hibernating underground. But they surface after summer storms to feed and breed in the rain pools. Their croaking choruses are reported to sound eerily similar to the bleating of dying lambs.

As October approaches, this year's monsoon season is coming to an end. But keep your eyes peeled for these and other monsoonal beasts as they embark on their final aboveground adventures before slipping, digging, and slithering back into the earth.

Marian Lyman Kirst is an intern for High Country News

Photos courtesy U.S. Fish and Wildlife Service, Jillian Cowles for USFWS and flickr users jclucier, treegrow, Aztec Lizard, Joachim S. Muller, and StarWatcher307.