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How to identify it
- Adults are very small, hump-backed flies with few veins in the wings, like other phorid (scuttle) flies.[1]
- Females have a hardened, external egg-laying organ (ovipositor) whose shape differs from species to species and is used to tell them apart. Males are sometimes smaller than females.[1]
- The best clue is behavior: the flies hover over fire ant workers near a disturbed mound and dart in to strike an ant, often in less than a second. They are found only around disturbed fire ant mounds.[1]
- Parasitized ants usually end up as detached heads; the fly pupates inside the empty head, with two small breathing horns poking out from the sides.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Other phorid flies | Most phorids that people notice breed in decaying matter, and some become household pests. Decapitating flies are not attracted to people, pets, rotting material, carrion, feces, fruits, vegetables or prepared foods.[1] |
Where it lives
Pseudacteon flies attack ants worldwide, with about two dozen species on fire ants in South America. In the US, the released P. tricuspis and P. curvatus cover most of the Southeast; P. obtusus is abundant in much of Texas and Florida, with smaller populations in Mississippi and Georgia; P. litoralis (Alabama) and P. nocens (Texas) have limited but expanding ranges; and P. cultellatus is established at two Florida sites. P. tricuspis has spread slowly and often failed to establish in the more northern parts of the fire ant range.[1][2]
Biology and life cycle
A mated female hovers over foraging fire ant workers and strikes one in the thorax with her ovipositor, laying an egg inside the ant.[1]
The maggot moves into the ant's head and feeds mostly on its blood (hemolymph). Before pupating it releases a chemical, likely an enzyme, that loosens the joints of the ant's shell, eats out the contents of the head, and the head usually falls off. The maggot then pushes off the ant's mouthparts and pupates inside the head, its hardened front end plugging the mouth opening.[1]
Adults emerge 2 to 6 weeks after pupation. The whole life cycle takes 4 to 12 weeks depending on temperature, and adults live only 3 to 5 days.[1]
In several species, the size of the ant's head decides the sex of the fly: large ants produce females and small ants produce males.[1]
Each species is highly host specific, attacking only one ant species or a group of closely related ones. The released species mainly attack the red imported fire ant; P. litoralis and P. curvatus also attack the black imported fire ant and hybrids.[1][3]
Damage and signs
- They are beneficial. Besides killing the ants they parasitize, the flies disrupt fire ant foraging, because workers stop to defend themselves or hide when the flies are near, and they shift competition between fire ants and other ants.[1][3]
- Their overall effect on fire ant populations may be limited, because fire ant workers have evolved ways to cope with the parasites.[3]
Health risk
They are not attracted to people or to animals other than ants, or to food, garbage or carrion; the sources describe them only as parasites of ants.[1][3]
Control
Prevention
No control is needed. These flies are biological control agents for imported fire ants and are found only around fire ant mounds.[1][2]
Biological control
USDA-ARS, the University of Texas and USDA-APHIS, working with 11 states, released six species at many sites across the southern US beginning in 1997. Fire ant biological control also uses microsporidia, viruses and other parasites.[1]
Common questions
- Do decapitating flies really cut off fire ant heads?
- In effect, yes. The maggot develops inside the ant's head, dissolves the membranes holding it together and eats the contents, and the head usually falls off. The fly then finishes developing inside the detached head.[1]
- Will decapitating flies get rid of fire ants in my yard?
- Not on their own. They kill some ants and disrupt foraging, but fire ant workers have evolved ways to cope with them, which may limit their effect on fire ant populations.[1][3]
- Will these flies bother people or get into food?
- No. They are attracted only to fire ants, not to people, pets, food or garbage.[1]
Sources
- University of Florida/IFAS Extension (Featured Creatures), “Fire Ant Decapitating Flies Pseudacteon spp., EENY680 (A. McCorquodale, J. P. Cuda and S. D. Porter; May 2017).” journals.flvc.org/edis/article/view/124900 (accessed 2026-11-09)
- Journal of Insect Science (via NCBI PubMed), “Fire ant decapitating fly cooperative release programs (1994-2008): two Pseudacteon species, P. tricuspis and P. curvatus, rapidly expand across imported fire ant populations in the southeastern United States (A. M. Callcott et al.; Journal of Insect Science 11: 19, 2011; abstract).” pubmed.ncbi.nlm.nih.gov/21526930/ (accessed 2026-11-09)
- Annual Review of Entomology (via NCBI PubMed), “Pseudacteon Phorid Flies: Host Specificity and Impacts on Solenopsis Fire Ants (L. Chen and H. Y. Fadamiro; Annual Review of Entomology, 2018; abstract).” pubmed.ncbi.nlm.nih.gov/28938082/ (accessed 2026-11-09)
- iNaturalist, “Pseudacteon taxon page (order and family).” www.inaturalist.org/taxa/504017 (accessed 2026-11-09)