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.
Arizona ranks 3rd 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 bu
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.
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
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 r
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 sensor
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.
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