Plains Spadefoot

Spea bombifrons

(Scaphiopus bombifrons)

Plains Spadefoot

Distribution in Wyoming

 

 

 

 

 

 

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The Plains Spadefoot is distributed across the southern middle edge of Canada into Montana and North Dakota, then south through the plains to Texas and into the northern tip of Mexico. In Wyoming its range reaches from the eastern counties, westward between the Laramie Range and the Big Horn Mountains, into the Big Horn Basin. It inhabits the grassland and sagebrush communities of the prairie life zone below 6,000 feet where it prefers the easy burrowing of friable soils and sandy loams in the floodplains and the low lying regions between gentle hills. There is some distribution overlap sympatric) with the Great Basin Spadefoot in the Beaver Divide and the Rattlesnake Hills areas of Fremont and Natrona counties.

Plains Spadefoot Plains Spadefoot

The spadefoot is primarily nocturnal with large globular eyes and cat-like elliptical slits for pupils; lying between these orbits is a round and bony bump—the boss. Its pale moist skin is gritty from glandular eruptions. The dorsal surface is a plastered, washed-out gray or watered-down brown and pocked with patches of green scattered amongst the orange tinted glands. The head is foreshortened and its snout handsomely protrudes beyond the smaller and slightly recessed lower jaw. To the rear of the eye and just above the shoulder is the small and inconspicuous tympanum—a protective membrane cover that helps transmit vibrations to the tympanic membrane of the inner ear. The webbed rear feet each own a single metatarsal cutting tubercle or spade, from which its surname is derived. Assisted by these spades, it burrows by ratcheting the body back and forth while shuffling the feet—backing its way down into the soil.

Plains Spadefoot Plains Spadefoot

The species is identified from the Great Basin Spadefoot by having a larger, more conspicuous and bony boss and by its shorter and broader cutting tubercle. (These are subtle characteristics and you need a bit of experience or each species in-hand to note the differences.) It is identified from true toads by lacking a parotoid gland, having a single cutting tubercle, and by its elliptical pupils.

Plains Spadefoot Plains Spadefoot

Their explosive breeding cycle begins as an immediate response to heavy rains. Breeding aggregations quickly assemble along the newly formed temporary pools and activity is greatest during the first or second night. Males have a vocal sac on each side of the throat (they appear merged into one sac like a ping-pong ball) and these are stretched and inflated when issuing a resonating, nasal (duck-like) snore to attract receptive females. Calling males may wrestle to defend their territories or in attempts to dislodge other males already paired in amplexus. Males have black cornifications (nuptial pads) along the digit margins of the front feet and these are used to help seduce and hold a mate. Females are grasped around the waist (pelvic amplexus) and release a mass of 200-300 eggs which are fertilized as they are attached to the submerged vegetation. Most eggs hatch within 1-2 days and it takes the developing tadpoles another 3-5 weeks for metamorphosis to occur. However, some tadpoles are genetically predisposed cannibals and they exhibit faster growth because of the increased nutrition obtained by eating their fleshy associates. This accelerated development and metamorphosis may take place in as little as 2 weeks. Sexual maturity is reached in the next 1-2 years.