Overview
The Small-mouthed Salamander (Ambystoma texanum) is a secretive, subterranean mole salamander native to the rich, damp river bottomlands and floodplains of the central United States. Named for its disproportionately tiny head, blunt conical snout, and narrow jawline that sets it apart from all other members of the family Ambystomatidae, this smooth-skinned burrower spends nearly its entire adult life concealed deep underground, emerging under the cover of torrential late-winter rains to perform mass breeding migrations to woodland vernal pools.
Biology and Physical Characteristics
Ambystoma texanum possesses a stout, robust body with 14 to 15 prominent costal grooves running vertically along its flanks. Its skin is smooth and moist, colored a handsome dark slate-grey, charcoal-black, or purplish-brown, profusely flecked with irregular, lichen-like blotches of silvery-grey or pale blue along its sides and limbs. Its most diagnostic evolutionary trademark is its remarkably small, short head: unlike the broad, shovel-headed profiles of its close relative the Tiger Salamander, the head of the Small-mouthed Salamander is narrow and compact, with an abbreviated snout and tiny mouth adapted for grabbing subterranean earthworms in narrow underground tunnels.
Behavior and Ecology
A fossorial specialist, the Small-mouthed Salamander utilizes its blunt snout and strong limbs to burrow through soft, damp floodplain soil or inhabit abandoned crawfish and rodent tunnels. In late winter or early spring (often January through March), rising temperatures and soaking night rains trigger an explosive mass breeding migration. Hundreds of salamanders emerge from underground to march toward fish-free vernal pools and sluggish floodplain ditches. Females attach small, gelatinous egg clusters to submerged sticks and dead leaves. The aquatic larvae hatch with external gills, feeding ravenously on mosquito larvae and daphnia before metamorphosing into terrestrial juveniles by midsummer.
Conservation and Human Impact
The Small-mouthed Salamander is classified as Least Concern on the IUCN Red List. Due to its wide geographic distribution across the Mississippi Valley and tolerance for semi-disturbed woodlots and agricultural ditches, it remains locally common. However, the draining of seasonal wetlands, clearing of bottomland hardwood forests, and agricultural pesticide runoff present ongoing localized threats, particularly near the northern periphery of its range in the Great Lakes region.
Interesting Factoid
The Small-mouthed Salamander has a head so surprisingly tiny compared to its plump body that it looks like it was born with the head of a different, much smaller salamander!