Night of the Toads

I was fortunate enough to attend the annual Invertebrates in Education and Conservation Conference in Rio Rico late last month, and participate in a couple of the spontaneous field trips that happen, especially after dark. One such excursion, led by my good friend Zack Lemann of the Audubon Institute Insectarium in New Orleans. We were looking for certain beetles, and had success, but reptiles and amphibians were also in abundance. Chief among those were toads.

We drove north from the conference headquarters in Rio Rico toward Madera Canyon, stopping at a service station at an exit in Green Valley. There, right by the interstate, we found the cactus longhorn beetles Zack was after, but there were also several Couch’s Spadefoots (Scaphiopus couchi) dining on the many insects drawn to the lights of the gas station.

Spadefoots are technically frogs in the family Pelobatidae. They lack the large parotoid glands of true toads (located just behind the eyes and visible as large, elliptical bulges). What truly sets them apart from other amphibians, however, is the dark, hardened tubercle on the underside of the heel of each hind foot. These “spades” help the animal dig into and out of the mud.

Couch’s Spadefoot is exceedingly tolerant of long dry spells, emerging during the soaking monsoon downpours that typically begin in early or mid-July here in the Sonoran Desert. They erupt from low-lying areas as those ditches and depressions fill with water and soak into the soil, softening it. The spadefoots have been buried fairly deep in the soil awaiting the rains.

Males call to females with a voice that has been likened to a “bleating sheep with a cold.” Real attractive. It works, though, at least on female spadefoots. Females lay eggs in the temporary puddles and the ova hatch twelve to twenty-four hours later. The tadpoles, in a race against the evaporation of their aquatic niche, metamorphose to miniature adults in as little as eight days. Before the mud dries and cracks, the spadefoots dig in. Underground they are able to tolerate at least a year without food or water until the rains once again return.

From Green Valley, our party moved on to a retirement community in the small town of Continental. The lights in the parking lots of the community attract many insects, and not surprisingly toads are wise to this fact. Under one light I found this Great Plains Toad, Bufo cognatus.

I am grateful that the toad was quiet, for I have read that the calls of males are lengthy, extremely loud, and likened to a jackhammer. Unlike spadefoots, members of the genus Bufo are true toads in the family Bufonidae, characterized by “warty” skin and those prominent parotoid glands. Otherwise, the life cycle and habits of the Great Plains Toad closely resembles that of Couch’s Spadefoot. The tadpoles take longer to mature, but the adult toads likewise spend the bulk of their lives underground awaiting heavy rains. They make the most of their time aboveground, eating a huge amount of insect and arachnid prey to get them through lean times.

Conspicuously absent from the landscape on this particular night (July 28-29) were the enormous Sonoran Desert Toads, Bufo alvarius that usually dominate the scene. Formerly known as the Colorado River Toad, this species has apparently been rendered extinct in much of the Colorado River corridor (along with the water which now does not even reach the Gulf of Mexico). These are huge animals, mature adults often measuring seven inches….in just about any direction so great is their girth. Some specimens would find a dinner plate a somewhat confining perch. They are not easy to photograph, either, as they turn away from flashes. I imaged this one in Picture Rocks.

Sonoran Desert Toads are nothing to trifle with, especially if you are a dog. They have incredibly toxic skin secretions. The hallucinogenic properties of those toxins are well-known to the medical community, too. Stupid people who engage in “toad-licking” get what they deserve. Pets that don’t know better can die from ingested toad toxins.

A really great online article about the Sonoran Desert Toad can be found here at The Firefly Forest website. Information about the other anurans (science-speak for “frogs and toads”) treated here can be found on the website of the Arizona-Sonora Desert Museum.

Sources:
Brennan, Thomas C. & Andrew T. Holycross. 2006. Amphibians and Reptiles in Arizona. Phoenix: Arizona Game & Fish Department. 150 pp.
Hanson, Jonathan and Roseann. 1997. Fifty Common Reptiles & Amphibians of the Southwest. Tucson: Southwest Parks and Monuments Association. 63 pp.