They may be tiny, but these ants have an impressive defense mechanism—they skip the biting and spray their attackers with acid instead.
Several species of ants defend themselves and their colonies by spraying formic acid from their abdomens directly into the eyes of predators (or any animal in their way, really.) Though harmless to humans in low concentrations, the acid can burn the skin of small animals and cause blindness, and victims generally end up starving to death.
Yellow crazy ants, in particular, are one of the most ruthless acid-slingers of the bunch; they’re single-handedly destroying ecosystems in Australia and numerous Pacific islands by wiping out native wildlife with their aggressive — and often unprovoked — acid attacks. The notorious invaders likely originated from West Africa, crossing oceans on driftwood or vessels. They’ve now gotten so prolific that the United States government had to create “Crazy Ant Strike Teams” in an effort to take them out.
Like wood ants, crazy ants often form dense and aggressive supercolonies, decimating numerous plants and animals in their wake.
On Johnston Atoll, an island refuge in the North Pacific, ground-nesting shorebirds continue to suffer from an ongoing infestation. Alisa Opar, an editor at Audubon Magazine, described a horrific scene that scientists witnessed on the island several years ago:
“[B]irds in the infested zone looked like zombies. They were sluggish, twitching as ants crawled over them. Their acid-burned eyes were swollen shut and blinded.”
Baby birds, who instinctually stay put in their nests until they are mature, are particularly susceptible to the ants’ attacks.
Other acid-spraying ant species deploy this chemical weapon in interesting ways: for example, tawny crazy ants use it as an antidote to the toxic venom of rival fire ants by rubbing themselves with their own formic-acid filled venom during fights.
The name for formic acid actually comes from formica, the Latin word for ant. The acid was apparently first extracted from ants in the 17th century by English naturalist John Ray who distilled the poor insects.