[2] In October 2008, it was declared extinct by the International Union for Conservation of Nature since the species had not been seen since 1987, despite years of extensive searches.

[7] Incilius holdridgei tadpoles are small in size with ovoid-shaped bodies that are dark brown in color and feature a lighter venter surface.

Due to their morphology, Incilius holdridgei are deaf and mute; they apparently do not communicate through sound or have mating calls- a rarity among frogs and toads.

Before 1986, the species had been relatively easy to spot during its two-month mating season from April to May when males and females became more active and gathered in the hundreds.

From collected past and new research along, as the Holdridge's is exposed to Costa Rica's rainforests' bacteria and fungus, the diet can be inferred.

The Holdridge's toads' diet includes a broad range of arthropod invertebrates, among them spiders, larval stages of moths and butterflies (lepidopterans), flies, beetles, earwigs (dermoptera), ants, and mites (Savage 2002).

[5] In reference to the reproduction of the Holdridge's toad, it was expressed as an "explosive breeder"[9] It acquired this title because it produced eggs in forest floor pools.

[1] Multiple causes are believed to have led to the toad's presumed extinction, including chytridiomycosis, climate change, and deforestation.

[6] The main threat to Holdridge's toad is thought to be chytridiomycosis, a fungal pathogen, Batrachochytrium dendrobatidis, that causes an infections disease in amphibians.

[11] High levels of this fungus were detected in the breeding grounds of Holdridge's toad before and after the species appeared to vanish.

[12] Juveniles were found, indicating relatively recent reproductive activity, but no large aggregations were seen; this species should be considered Critically Endangered.

[15] Much of the known range of this species is protected in Parque Nacional Braulio Carrillo, 20 km north-east of the capital of San José.

The two sites where the species is known to persist in 2010 are located in the Cerro Dantos and Jaguarundi Refuges, neither of which has the same protection status as a national park.

[1] A monitoring project is being carried out under the auspices of the Foundation Mohamed Bin Zayed Species Conservation Fund.