It’s been reported that the common fruit fly, Drosophila melanogaster, drinks alcohol to kill the wasps that have hatched inside of its body, which would otherwise eat it alive.
Drosophila melanogaster gets the alcohol from eating yeasts that grow on rotting fruit that can contain up to 6% alcohol. The flies have even developed a certain degree of resistance to alcohol, but the flies tolerate it since it’s medicine.
Insects are plagued by parasitic wasps, which lay eggs in or on their bodies, turning them into living larders for their developing young. The grubs eat their hosts from the inside out, eventually bursting out of their dead or dying husks.
Neil Milan, from Emory University, conducted an experiment where he fed fly larvae food that contained 6% alcohol. He then offered the larvae to Leptopilina heterotoma. The wasps laid three times as many eggs on the flies that hadn’t ingested any alcohol.
Milan published his findings in the journal Current Biology and found that twice as many wasp grubs die if their hosts ingest alcohol. Even survivors fare badly. Milan also discovered that infected larvae will actively seek to medicate themselves with alcohol.
Leptopilina boulardi, another type of wasp, has evolved a resistance to alcohol and fares better than L. heterotoma.
Flies join humans, chimps, other primates, tapirs, macaws, woolly bear caterpillars and other animals that medicate themselves.
Reference: “Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly” by Neil F. Milan, Balint Z. Kacsoh and Todd A. Schlenke, 16 February 2012, Current Biology.