Phorid Flies

Phorid flies are known to parasitize ants. The common means of parasitism, and until recently thought to be the only method, is as follows. A gravid female phorid fly seeks out foraging ants to parasitize, and most flies appear to specialize on specific species of ants or at least a group of congeners. Once found the female attacks host workers and injects eggs into their head. The egg hatches, feeds from the ant that is hosting it and eventually pupates. In many cases the fly emerges from its pupal case in such a way that it causes the ant's head to pop off.

Recently it was discovered there is another method of ant decapitation. Some adult phorids were observed sawing the heads off of injured Odontamachus ants. Presumably the ant heads are used for food by the adult flies.

Pseudacteon
Pereir et al. (2015) - The genus Pseudacteon Coquillett (Diptera, Phoridae) has a worldwide distribution and comprises parasitic myrmecophilous species that decapitate host ants. Seventy three species are known in the genus with 41 of them occurring in the Neotropical Region.