This member of the genus Elachistocleis is characterized by an ovoid, robust body shape with a small, narrow head ending in a prominent, pointed snout. Adults are small, with snout-vent lengths ranging between 23 and 32 mm in males, whereas females are slightly larger, reaching 27 to 36 mm. The skin is entirely smooth. Dorsal coloration of Elachistocleis bicolor is uniform, varying from dark gray to olive-brown, sometimes featuring a thin, pale vertebral stripe. Its most diagnostic feature is the striking ventral contrast, displaying a bright yellow or orange belly, usually immaculate, which contrasts dramatically with the dark dorsal surface. There is a distinctive post-ocular dermal fold across the head, and the external tympanum is completely absent.

Geographical distribution: Widely distributed across the lowlands of southern South America. Its geographic range extends throughout central and northern Argentina (reaching as far south as the Buenos Aires province), across the entirety of Uruguay, most of Paraguay, eastern Bolivia, and vast regions of central and southern Brazil, including states such as Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, and Mato Grosso do Sul.

Habitat: Primarily inhabits open lowland ecoregions, such as the humid and dry Chaco, the Pampas, the Espinal, and parts of the Cerrado and Pantanal. It is highly associated with temporary wetlands, seasonally flooded grasslands, shrubby savannas, agricultural fields, and cattle pastures. This adaptability allows it to persist in human-modified landscapes, provided temporary freshwater bodies are available for breeding.

Feeding: Exhibits a highly specialized diet, being strictly myrmecophagous. It feeds almost exclusively on ants and termites. Its small head and narrow snout are specialized adaptations that allow it to penetrate tiny subterranean tunnels and termite mounds, capturing prey efficiently with its rapid, sticky tongue.

Behavior: Features highly fossorial and secretive habits. During dry or cold periods, it remains buried underground or hidden beneath decomposing logs, rocks, and dense leaf litter, entering a state of estivation. Surface activity is mainly nocturnal and tightly synchronized with heavy rainfall during spring and summer, when individuals emerge in large numbers.

Reproduction: Described as an explosive breeder, with reproductive activity triggered immediately by heavy rains during warm seasons. Males call while floating on the water surface, anchored to emergent vegetation along the margins of temporary pools. The advertisement call is a long, high-pitched metallic buzz, resembling the sound of an orthopteran insect. Females lay hundreds of pigmented eggs in a floating gelatinous film on the water surface. Larval development is rapid, an essential evolutionary adaptation to complete metamorphosis before temporary pools dry up.

Conservation status: Classified as Least Concern (LC) on the IUCN Red List. Despite ongoing habitat fragmentation due to agricultural expansion and urbanization throughout its range, its populations remain stable and show high tolerance to moderate anthropogenic disturbances, making it a common species across most of its distribution.