Large adult Mexican spadefoots are about 2.5 inches in length. They are brown, grayish-green, or grayish-brown with dark spots or blotches on the back. Faint light stripes may be present on the back and sides, and red-tipped tubercles are scattered over the back and head. Like other spadefoots, the Mexican spadefoot has large eyes and a short wedge-shaped horny tubercle on the bottom of each hind foot, which it uses to dig its way into the ground. Tadpoles have broad, flat heads with eyes high on the head. They can grow to nearly 3 inches, but most metamorphose before reaching 1.5 inches. Dorsally, tadpoles are light gray to olive or brownish-olive in color. Both carnivorous and omnivorous tadpoles occur; the former is induced by eating fairy shrimp and develop an exceptionally broad head, large jaw muscles, and a short gut.
Similar Species:
It is similar to the Plains spadefoot; but Mexican spadefoots lack a boss between the eyes (Plains spadefoots have a bony boss). Mexican spadefoots smell like peanuts when handled (Plains spadefoots do not).
Habitat:
The Mexican spadefoot is characteristic of a broad range of habitats, from Chihuahuan Desert scrub, and semi-desert grasslands to Great Basin Desert scrub, Plains and Great Basin grasslands, and coniferous woodlands. It can be found on the edges of agriculture.
Behavior:
Primarily nocturnal, but metamorphs may be active by day. This species remains buried in soil for months and then emerges with the onset of the summer monsoon season to breed. Post-breeding, Mexican spadefoots can be found far from breeding ponds and will stay active as long as conditions remain moist and warm. Individuals probably do not maintain territories.
Hibernation:
Underground during cool months.
Reproduction:
This spadefoot breeds in temporary rain pools that fill during summer storms. The call is reminiscent of running a fingernail along the teeth of a comb. Males usually call from the middle of a pond, often swimming around without being anchored. Clutches average a bit more than 1,000 eggs and are laid in masses attached to vegetation or debris. Eggs hatch in 2-3 days and most tadpoles metamorphose in 12-19 days.
Diet:
Mexican spadefoots eat a variety of invertebrate prey, such as termites, ants, beetles, and spiders. They apparently avoid arthropods with toxins or chemical defenses, such as velvet ants and blister beetles.
