Acrobat ants (Crematogaster spp.) have a heart-shaped abdomen. When disturbed, they raise up their abdomens and ooze pungent formic acid at their attacker. (The name “formic acid” comes from the Latin word for ant, formica.) They eat aphids' honeydew, living and dead insects, protein from bird and other droppings, and sugary or meaty foods. Sometimes they build nests in people’s houses. There are about 30 species of acrobat ants in North America.