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Spadefoot toads — a sudden abundance
Last updated on Wednesday, January 01, 2003
My husband Richard and I sat in our backyard one summer evening, watching a violet-black thundercloud drift downhill, trailing dense curtains of rain. Brilliant stabs of lightning punctuated the early darkness. As the storm drew closer, a distant sound, like sheep bleating, began to insinuate itself through the banging thunder and the nearby car traffic - spadefoot toads! The downpour had brought the spadefoot toads up from the soil to feed and call for mates.
These tiny amphibians are a paradox: out of water, they dehydrate quickly, and their gilled tadpoles are aquatic; yet they are most abundant in the Southwest's deserts. How do they manage?
Spadefoots spend much of their lives - years, in extreme droughts - dug deep under the soil surface, barely respiring, dormant. But after heavy summer rains, they emerge in noisy abundance. Roused by the sound waves of thunder, the toads tunnel upwards at night from solitary burrows as deep as two feet below the surface, hop to the nearest water - puddles, temporary ponds, roadside ditches - and squat, rehydrating their parched bodies through a porous skin patch on their bellies. Males float and bellow their desire; the curious trills and bleats of thousands of tiny swelling throats carry for miles. Females, drawn to the din, find a mate: The two float while he clambers atop her and squirts sperm over the eggs she exudes.
At dawn, the adults dig themselves back underground with their "spades": black, sharp-edged scrapers on the underside of each hind leg. They seem to swim backwards into the soil, wiggling from side to side as each powerful hind foot alternately pushes dirt outwards. When monsoon season passes, the toads retreat deeper underground to wait, dormant, until summoned again by reverberating thunder.
Left behind in ponds and puddles are the fruits of their hurried mating. If all goes well, the eggs hatch within a day, and the tiny, black tadpoles feed energetically on plants, small aquatic animals, and sometimes each other, racing to mature into air-breathing adults before their watery world dries up. Couch's spadefoot - the type that sound like bleating sheep - sprint from egg to adult in just over a week! (By comparison, bullfrog tadpoles take two leisurely years.) Surviving tads emerge from their puddle, gulping air and still dragging their tail, and follow their parents into the earth.
When the rain faded to a gentle patter, we took a flashlight and walked through our subdivision. Across the busy road, past wet fields of cotton, the sound swelled around us. At the edge of a normally dry flood catchment basin, we shone a flashlight into dark water. Below us hundreds of tiny toads floated, their throats swelling and shrinking, swelling and shrinking. We walked home again, wet, and overjoyed at the miracle of rain and toads in the New Mexico desert.
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