0 an acid with the chemical formula HCOOH, which is found naturally in some insects and plants that sting (= cause a small, painful skin injury):
If alarmed, the caterpillar squirts formic acid.
Pine martens dive into these ant heaps, grab as many grubs as they can, and get out quick before the ants can spray them with formic acid.
In the liver, enzymes turn methanol into formaldehyde, then into formic acid.
Tests revealed the paint remover contained formic acid, which an expert said could be lethal to a child if only a teaspoonful was swallowed.
