Biodiversity Data Journal : Taxonomic paper
A new type of ant-decapitation in the Phoridae (Insecta: Diptera)
Corresponding author: Brian V. Brown (firstname.lastname@example.org)
Academic editor: Anu Veijalainen
Received: 06 Dec 2014 | Accepted: 31 Dec 2014 | Published: 02 Jan 2015
© 2015 Brian V. Brown, Giar-Ann Kung, Wendy Porras.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0) which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Brown B, Kung G, Porras W (2015) A new type of ant-decapitation in the Phoridae (Insecta: Diptera). Biodiversity Data Journal 3: e4299. doi: 10.3897/BDJ.3.e4299
The genus Dohrniphora is a hyperdiverse group of phorid flies, a family whose species are commonly characterized as generalized scavengers. The lifestyle of most species of Dohrniphora is unknown, although one cosmopolitan, synanthropic species, D. cornuta (Bigot) fits the general scavenger mold. Here we show that flies of the D. longirostrata species group exhibit highly specific “headhunting” behavior in which injured Odontomachus ants are decapitated, the heads dragged away, and females either feed on their contents or lay an egg nearby. Since most females studied lacked eggs in their ovaries, we conclude that this bizarrely specialized feeding is necessary to provide nutrients for reproduction in these flies. Our study provides further evidence that injured ants are a common, stable resource in tropical ecosystems that support a wide array of phorid flies. Such narrowly constrained lifestyles, as exemplified by exclusively feeding on and breeding in the head contents of certain ponerine worker ants, could allow the co-existence of a huge community of saprophagous flies.
Tropical, behavior, Dohrniphora, Formicidae, specialized saprophagy.
The Phoridae are a family of over 4,000 species of small (0.4-6.0 mm) poorly-known flies, with an incredible diversity of lifestyles.
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 (Phorinae). The description of this lifestyle is based on earlier observations by us (
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- 21.45°S, 46.34°W), La Cangreja National Park in Costa Rica (LC- 9.68°N, 84.39°W), and La Suerre in Costa Rica (LS- 10.13°N, 83.73°W). At these sites, we observed the interaction of female Dohrniphora longirostrata (Enderlein) (CV), D. oricilla Kung & Brown (LC), and D. conlanorum Kung & Brown (LS) with experimentally injured (crushed with forceps) host ants Odontomachus chelifer (Latreille) (CV), O. erythrocephalus Emery (LS), and O. baueri Emery (LC). Observations were made throughout the day, but flies were found to be most active at dusk. Voucher specimens of both flies and ants are deposited in the Natural History Museum of Los Angeles County (LACM), as follows: D. conlanorum [catalog # LACM ENT 050969], D. longirostrata [LACM ENT 059215], D. oricilla [LACM ENT 212894] O. chelifer [LACM ENT 038451], O. erythrocephalus [LACM ENT 256234], O. baueri [LACM ENT 305128].
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 Odontomachus.
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 D. oricilla, but might have been overlooked in other species. Next, the fly approached the ant, darting in to touch it occasionally, still circling it. Occasionally, flies would grasp antennae or legs and rapidly pull on them (
A female of D. oricilla assessing injured Odontomachus ants at La Cangreja NP, Costa Rica.
A female of D. conlanorum processing and eventually decapitating an injured Odontomachus ant at La Suirre, Costa Rica.
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 (
A female of D. oricilla cutting the head off an injured Odontomachus ant at La Cangreja NP, Costa Rica.
Eventually, the ant's head became loosened and after some tugging (
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 (Insecta: Orthoptera) placed in the same cages were ignored by flies.
Apparently, healthy ants are not subject to attack by Dohrniphora females. Under laboratory conditions, caged flies were frequently captured and crushed by ants (
Females of the Dohrniphora longirostrata species group are distinctive because of their greatly elongated proboscis, which is almost as long as their entire body (
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 Dohrniphora require feeding on the contents of Odontomachus heads in order to mature their eggs.
Females of the Dohrniphora longirostrata group decapitate injured Odontomachus ants in tropical Central and South America, both for their larvae but apparently also to feed themselves and allow development of eggs. Such feeding behavior is known for other non-gravid parasitoid flies feeding on their injured host ants (
It is common in tropical forests for up to 50-100 species of Dohrniphora to be co-existing (
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.