What acid occurs naturally in most ants?

Formic acid, systemically named methanoic acid, is the simplest carboxylic acid. The chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in most ants. The word "formic" comes from the Latin word for ant, formica, referring to its early isolation by the distillation of ant bodies, and the trivial name in some languages means "ant-acid", such as Dutch mierenzuur, Danish myresyre, Faroese meyrusýra, Français acide formique and German Ameisensäure. Esters, salts, and the anions derived from formic acid are called formates.

In nature, it is found in most ants. The wood ants from the genus Formica can spray formic acid on their prey or to defend the nest. It is also known from the trichomes of stinging nettle (Urtica dioica). Formic acid is a naturally occurring component of the atmosphere due primarily to forest emissions.