UF/IFAS Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972-2578

Phone: (863) 763-6469

E- mail:  dfculbert@ifas.ufl.edu

November 1,   2006

Quick Links:   Phorid Fly    Ant Nests     Predator Spread   References    
 Feature Article - for release the week of November 5, 2006

Dan Culbert - Extension Horticulture Agent

Beware the Headless Fire Ant


I know that Halloween is past, but one of my favorite fall legends is the Legend of Sleepy Hollow, written by Washington Irving in the early 1800s.  In this story, the headless horseman scares the wits out of the lowly love-scorned teacher, Ichabod Crane. 

 It seems that this legend may soon be updated in our area with a new title: the headless fire ant, as written by an introduced predatory insect, the Phorid Fly.  Our office has begun working with a few ranchers and FDACS officials to release this fearful predator. As these fiendish flies begin to spread over our region, they will help reduce that burning, itching pest of our pastures and Florida Yards.

Okeechobee Livestock Agent Pat Hogue recently received his first shipment of decapitated fire ant heads infested with lots of squirmy maggots.  They are the larva of a very small gnat-like fly, Pseudacteon tricuspis, a native of Argentina.  And last Wednesday, the battle began with the first release of the emerging adult flies that have begun to dive bomb fire ants here in Okeechobee.

Phorid flies are very small, about the size of an ant's head. Under magnification, the flies have big eyes and a sort of humped back.  ('Humpbacked' flies are one of the common names for this family.)   Females have an elaborate egg-laying ovipositor on their abdomen that is used to stick it to the Fire ant.  But it will take a careful eye to even know they are there, as they appear as small fuzzy specks hovering over host ants.

This is a Phorid Fly (Pseudacteon tricuspis) which is being released in the  Okeechobee area over the next month. Photo: Lyle Buss, UF/IFAS 

    A Phorid Fly (arrow) hovers over the ants before dive-bombing and sticking an egg into the ant's mid-section.  Photo:  Larry Gilbert Inside the head, the maggot causes the fire ant head to fall off, killing the ant. 

Inside the head, the maggot causes the fire ant head to fall off, killing the ant Photo: USDA

The maggot pupates inside the head, and the adult fly squeezes out the ant's mouth. The maggot pupates inside the head, and the adult fly squeezes out the ant's mouth. Photo: USDA

The life cycle of this fly is pretty graphic.  Female flies that are released near mounds will dive bomb the fire ants and lay their eggs inside them.  The egg hatches into a tiny maggot that burrows inside the ant and moves to the antís head. Inside the head, the feeding maggot eventually causes the fire ant head to fall off, killing the ant. The maggot pupates inside the head, and the adult fly squeezes out the ant's mouth.

Each newly emerged female fly can attack and kill 200 to 300 more ants.  While the number of actual ants killed is not large, the attacking phorid flies are a concern to the remaining fire ants.   Instead of marching all over the place looking for food, the colony changes its behavior because workers now must hide to avoid attack by flies. A good guess is that ant nests with phorid flies will only collect half the amount of food they would normally retrieve.  When ants hide, their colony starves and weakens, so Fire ants do not spread.

A large single Fire Ant  mound indicates there is only one queen and the workers are larger in size. Photo:  Dan Culbert, UF/IFAS

This mound in St.Augustinegrass grass has multiple entrances and is typical of a multiple queen (polygyne) nest. The ants will be smaller in size in this mound. Photo: Rudolf Scheffrahn, UF/IFAS

Finding the right spot

One of the challenges in a successful release program is to make sure these predatory flies have the greatest chance to gain a foothold so they can spread into new areas.  Scientists have found in the laboratory and in other field releases that larger sized worker ants will be an easier target for these phorid flies. 

Entomologists have discovered that some Fire ant nests are made of multiple queen colonies, while others have a single queen.  Single queen colonies have larger-sized worker ants.  They can be identified by large single mounds of disturbed soil.  These are the kinds of Fire ant colonies targeted during release programs.

Among phorid flies, the sex is apparently determined by the environment.  Males are produced when there are lots of smaller ant workers, whereas females are produced from larger ant workers.  And since the goal is to get lots of female flies that will lay lots of eggs, this is another reason to choose the single mound ant colonies.

Another item on the site release checklist is the number of nests per acre.  Pat Hogue was able to locate a ranch in northwestern Okeechobee County that exceeded the minimum amount of 25 hills per acre Ė he was lucky (?) enough to count out more than 40 mounds in the release site, and had barely covered that first acre.  This means there will be plenty of ants to make the planned 20-30 releases.

When will they be in my yard?

Iím certain there are a number of readers who will want to know if they can volunteer their Yard or pasture for a project of this nature.  However, there are not enough flies to give them out to everybody.   The conditions needed to insure that they will stick around have to be just right.  Rest assured that these little creatures will soon be winging your way.  It is estimated that these flies will spread at the rate of about 10 miles a year.  And Pat will be checking up on our new friends for the next two years.

Last fall a release of this phorid fly was made in Orange County.   This spring these ant predators were released in Fort Pierce and Sarasota.  Reports from Arcadia indicate that flies have traveled from Sarasota and are now found in DeSoto County.  With a new colony in the north county and others just to the east and west, we will soon have a good number of headless fire ants in our area.

Some really neat videos and photos have been taken by UF and USDA Scientists.  Iíve placed computer links to these sites and more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on the Fire Ant Fly, please email us at okeechobee@ifas.ufl.edu or call us at 863-763-6469.  Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 3 PM on Tuesday afternoons.  


Trade names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean Last update: 11/02/2006 .  This page is maintained by Dan Culbert 

USDA Agricultural Research Services Web site on area wide suppression of fire ants.    


Briano, Juan.  Ouch! The Fire Ant Saga Continues.  AgResearch Magazine. Washington: USDA ARS, 9/99. http://www.ars.usda.gov/is/AR/archive/sep99/ant0999.htm

Collins, Laura  and Scheffrahn, Rudolf H.  Red imported fire ant (Featured Creatures) EENY-195.  Gainesville:  UF Department of Entomology & Nematology,  8/05. http://creatures.ifas.ufl.edu/urban/ants/red_imported_fire_ant.htm 

Croft, Amy and Swiers, Morgan. Phorid Fly and Fire Ant Rearing. Gainesville: FDACS/DPI, 2002. http://www.doacs.state.fl.us/pi/methods/fire-phorid.html  

Graham, L.C. and Pinkston, Charles.  Yet Another Toehold for Phorid Flies. Cullman, AL: Cooperative Extension Service, 3/4/03. http://www.aces.edu/dept/extcomm/newspaper/june4c03.html 

James, Shannon.  P. tricuspis Release Protocol.   Washington: USDA: 8/18/05.  http://cphst.aphis.usda.gov/projects/Phorid_monitoring/Phorid_text/tricuspis%20release%20protocol.pdf 

Morrison, Lloyd W.  Pseudacteon spp. (Diptera: Phoridae). Ithaca: Cornell University BioControl webpage, 2004. http://www.nysaes.cornell.edu/ent/biocontrol/parasitoids/pseudacteon.html 

Porter, Sanford D.,  Nogueira de Sa', Luiz Alexandre  and Morrison, Lloyd W.  Establishment and dispersal of the fire ant decapitating fly Pseudacteon tricuspis in North Florida. Biological Control Vol. 29, pp. 179Ė188,  6/03.  http://fireant.ifas.ufl.edu/publications/BC29_179.pdf 

Willcox,  Emma and Giuliano, William M. Red Imported Fire Ants and Their Impacts on Wildlife  (WEC 207).  Gainesville: UF/IFAS Extension Service, 4/06 http://edis.ifas.ufl.edu/UW242 

"I wonder if DEET will keep these biting flies off my back?"