Formic acid
Correct, formic acid causes the skin rash from stinging nettles and ant bites. Animals and plants secrete the acid for defense purposes. Formic acid is also found in the bites and stings of sawflies, wasps, and bees. Formic acid is the simplest carboxylic acid. Industrially, it is used in textile dyeing, leather tanning, and in coagulation of latex rubber. It is also used in the manufacture of fumigants, insecticides, and refrigerants.