Mexican Spadefoot (Spea multiplicata)

Photo by Young Cage

Mexican Spadefoot, Photo by Young Cage.

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Description

The Mexican Spadefoot is a moderate-sized (< 65 mm SVL) anuran, the dorsum of which is gray to brown with small dark blotches and red tubercles. Diffuse, light dorsal lines are present in some specimens.  The snout is blunt and rounded, the eyes are large, and the pupils are vertical.  The tympanum is present but small and inconspicuous.  Cranial crests, parotoid glands, and a boss or raised area between the eyes are all absent.  A dark, wedge-shaped tubercle, as wide as long, or nearly so, is present on the inside of the ventral surface of each hind foot.  When handled, this species smells of peanuts.  The Mexican and Plains Spadefoots are very similar in appearance.  See the species account for the latter species for specific differences.

In the 100-Mile Circle, the Mexican Spadefoot is known primarily from Sonoran desertscrub, Chihuahuan desertscrub, and semi-desert and Plains grasslands.  It occasionally ranges upslope into oak and pine-oak woodland.  Nearby to the south it occurs in foothills thornscrub.  It is widespread in the 100-Mile Circle, and absent only from the higher mountains and the western, drier deserts.  This species does not do well in agriculture, although it may be found on the agricultural interface with native vegetation.  It is known to penetrate into the urbanized areas of Tucson along desert washes.

The Mexican Spadefoot is an explosive breeder, emerging from its subterranean retreats with the first substantial summer storm to breed and forage at temporary rain pools. Breeding sites include ephemeral livestock tanks, playa lakes, ephemeral pools in arroyos, tinajas in canyons, roadside ditches, and other places where rain water collects.  Breeding sites can be found from low in the valleys upslope into montane canyons.  Males call while floating in water.  The call is reminiscent of running a finger along the stiff teeth of a comb.  The call note lasts about 0.75-1.5 seconds and is repeated over and over again. The call can be heard here: http://amphibiaweb.org/cgi-bin/amphib_query?special=call&genus=Spea&species=multiplicata

A clutch consists on average of about 1,070 eggs, and is attached to vegetation or debris in several cylindrical masses.  Eggs hatch in one or two days and metamorphosis occurs in 12 to >50 days depending on food availability and other environmental conditions.  Tadpoles have relatively short tails and large, blocky bodies with eyes oriented high on the head.  Larger tadpoles are colored from gray or olive to brown above; and typically they grow to 25-38 mm total length prior to metamorphosis.  Tadpoles occur in two morphs – carnivores and omnivores.  The former have broader heads and heavier jaw musculature, and if fairy shrimp are present, they develop rapidly by feeding on this rich resource.  They fare well in rapidly drying pools, but the omnivores metamorphose at a larger size and with greater body fat in pools that remain longer.  Metamorphs resemble adults, but measure 12-29 mm SVL.

The adults are nocturnal, but metamorphs may be found active by day.  Adults consume large numbers of winged and nymphal termites early in the monsoon season, then switch to available arthropods, such as beetles, bugs, ants, grasshoppers, and crickets.  Skin secretions of this species can cause sneezing and a runny nose in humans.

The conservation status of this species has not yet been assessed by the IUCN.  However, it appears to be fairly secure in our area, and no significant declines have been noted here or elsewhere within its range.  It is eliminated by agriculture and heavy urbanization or other major habitat disturbance; however, it has benefited from the construction of ephemeral livestock waters and other places that collect rain water.   Much of the literature on this species is under the name Scaphiopus hammondi, at a time when the Western Spadefoot (from California) and this species were thought to be conspecific.

Suggested Reading:

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Degenhardt, W.G., C.W. Painter, and A.H. Price. 1996.  Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque.

Dimmitt, M.A. 1992. Biology of desert toads with emphasis on spadefoots.  Pages 51-54 in Collected Papers of the Tucson Herpetological Society 1988-1991.

Morey, S.R. 2005. Spea multiplicata (Cope, 1863) Mexican Spadefoot.  Pages 519-522 in M.J. Lannoo (editor), Amphibian Declines: The Conservation Status of United States Species.  University of California Press, Berkeley.

Author: Jim Rorabaugh

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