Corresponding author: Brian V. Brown (
Academic editor: Anu Veijalainen
The genus
The
Here, we describe an entirely new type of ant decapitation, one that is otherwise unknown in any insect. Instead of decapitation caused by larval feeding, as in metopinines, our observation involves the activity of the adult female phorid of a different subfamily (
Observations were made in three places: forest fragments on a private coffee farm in southern Minas Gerais state in Brazil, near the town of Cabo Verde (CV-
All species of flies had similar behavior, documented in video clips. Approximately 10 decapitations per species have been observed. Flies arrived shortly after the ants were injured, usually arriving as in copula pairs in flight, cruising back and forth above the ants. After the pair landed, males immediately departed and females approached the injured
Female flies spent several minutes apparently assessing the degree of incapacitation of the ants. First, a fly would rapidly tap on undergrowth leaves with its body (“drumming”) while circling about 5 cm around the ant. This drumming behavior was observed only with
Eventually, flies climbed on the ant body, and began to probe with their mouthparts. Each fly concentrated on the occipital region of the ant body, using their mouthparts to probe deeply through the membrane (Fig.
Eventually, the ant's head became loosened and after some tugging (Fig.
Some flies (n=10) were captured, placed in a plastic tub with injured ants, and observed indoors. Most decapitated their hosts quickly in low light conditions, and fed upon the head capsule contents. On two occasions, flies laid a single egg 1 cm from the ant head. Injured crickets and grasshoppers (
Apparently, healthy ants are not subject to attack by
Females of the
We rarely observed oviposition in our study, but it originally seemed unlikely that the flies would be engaging in this ant-decapitating behavior for any other reason than to secure food for their larvae. A single ant head appears to be the required size for the development of the single fly larva. In captivity, however, the flies were usually observed feeding on the contents of ant head capsule. More strikingly, we dissected females arriving at the injured ants (n=16) and found no mature eggs in their ovaries. As these non-gravid flies could not possibly have oviposited, we therefore conclude that female
Females of the
It is common in tropical forests for up to 50-100 species of
For assistance in the field, we thank Lisa Gonzalez, Anna Holden, Kathryn Roach, and Inna Strazhnik, for technical support we thank Vladimir Berezovskiy and Weiping Xie, for constructive comments we thank Luis Chiappe and Anna Holden, and for funding we thank John Long and the National Science Foundation (NSF grants DEB-0516420 and DEB-1025922, both to B. Brown and P. Smith). Some video was taken by Kate Lain.
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Records of phorid flies attracted to injured arthropods from LACM collection
Data type: association records; full data available from discoverlife.org
File: oo_35167.csv