Wood ants (formica rufa group) form colonies that build huge nests made of piled-up pine needles. They’re one of many ant species whose bodies contain large amounts of formic acid, which smells like a cross between formaldehyde, Pine Sol, urine, and vinegar. That ammonia odor is why they’re sometimes called “piss ants.” And you’ll smell it especially when you squish an ant … or if they decide to spray it at you from glands in their abdomen (it’s a defense tactic when their nest is disturbed.)