Two-colored Oval Frog

Fascinating facts about the Two-colored Oval Frog

• Spanning from central Argentina up through Paraguay, Uruguay and into Amazonian Brazil, this microhylid thrives across South America, showing how a tiny amphibian can adapt to different climates.
• When the rains arrive, a single female can lay roughly 620 eggs that float on the water’s surface, linking clutch size directly to her body length of 27–36 mm. This direct size-egg relationship reveals how even minute frogs fine-tune their reproductive output to maximize survival chances.
• Males measure just 23–32 mm from snout to vent, while females grow slightly larger at 27–36 mm. Their diminutive size lets them slip into ant and termite nests to aestivate.
• Night-time hunters, these frogs devour mainly ants of the genera Pheidole and Solenopsis, but switch to termites during the inactive season in Uruguay. This seasonal diet flip demonstrates a flexible foraging strategy that keeps them well-fed year round.
• Beyond forests, they colonize seasonally flooded grasslands, rural gardens and urban backyards.

At a glance

About the Two-colored Oval Frog

The two-colored oval frog, Elachistocleis bicolor, is a diminutive microhylid that roams the grasslands and forests of central Argentina, Paraguay, Uruguay, and the Amazonian reaches of Brazil. At night the frog emerges, its brownish back blending with leaf litter while a vivid yellow belly flashes like a warning banner. Males measure 23–32 mm and females 27–36 mm from snout to vent, a size that belies their surprisingly robust diet. These frogs are semi-fossorial, slipping into the soil or taking refuge inside ant and termite nests during the dry season, a behavior that not only shields them from desiccation but also places them at the heart of their own food web. When the rains arrive, they abandon their subterranean hideaways to congregate in temporary pools, where the females lay roughly 620 eggs that drift lazily on the water’s surface, their numbers scaling with the size of the mother. Elachistocleis bicolor’s nocturnal foraging is a study in specialization: ants, particularly the genera Pheidole and Solenopsis, dominate its menu during the active season, while termites become the primary prey when the frogs are otherwise inactive. This dietary flexibility allows the species to thrive not only in pristine seasonally flooded grasslands and moist forests but also in human-altered landscapes such as rural gardens and urban parks. Their ability to aestivate within insect nests, coupled with a reproductive strategy timed to the wet season, illustrates a remarkable adaptation to the rhythmic pulse of South-American ecosystems, hinting at a resilience that has kept the species abundant across a broad range of habitats…

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