Ants and arthropods: Lycaenid caterpillars
Ants have mutualist associations with many different arthropods, many of which happen to be liquid feeding bugs (order Heteroptera). Honeydew is the liquid excretion of these insects, rich in sugar and very attractive to ants. A unique group of caterpillars in the family Lycaenidae (order Lepidoptera) secrete honeydew-like substances to attract ants. In fact, they have special organs dedicated to these liquid secretions. In exchange for the sugar rich liquid, ants protect caterpillars from parasitic wasps that would otherwise kill them.
But some caterpillars cheat! In an extreme way of using the ants for protection, some Lycaenids chemically mimic ant species, essentially send out a “lost young” signal. The ants take the parasitic caterpillars back to their nest site where the caterpillars chomp away on the brood. Who said there’s no free lunch?