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Flies That Decapitate Fire Ants?! They’re Real!

Most of us are all-too-familiar with fire ants (especially if you have ever lived in the southeastern United States). These ants form massive colonies, have a fiery sting, and aggressively attack people.

But nature has a way of balancing things out. For any given species, there is usually something else out there that wants to kill it. In the case of fire ants (at least the ones that live in the South), they have an epic mortal enemy – the ant-decapitating fly.

These parasitoid flies, members of the genus Pseudacteon, kill fire ants by taking their heads clean off!

Now you’re wondering “how does a fly decapitate an ant“?! Let’s get into it!

Parasitoids versus Parasites

Pseudacteon flies are parasitoids. While this sounds like a parasite, they are very different things. Parasites are pests like ticks or fleas that feed off another organism but don’t kill it. Instead, they camp out for as long as they need to and let the host go away relatively unharmed (though many parasites spread diseases).

Parasitoids also feed off another organism, but the result is death for the host… and it’s usually quite brutal!

For example, parasitoid wasps lay their eggs inside of caterpillars or other larvae and then burst from them once they’ve had a chance to feed and grow. If you need a visual, check out the clip below –

Parasitoids sound like they might be rare, but they are everywhere. There are millions of species of parasitoid wasps and flies, and there are even a scattered few parasitoid species in other orders like beetles or butterflies.

Another important detail about parasitoids is that they are host-specific, unlike predators. This means that a parasitoid will only attack one kind of insect.

This makes them potentially a lot more useful than predators for controlling pests. After all, a predator will eat often eat anything in sight, whether it’s a pest or not. A fly that only targets fire ants? Now we’re talking!

Life Cycle of an Ant-Decapitating Fly

The life cycle of Pseudacteon flies is like something out of an alien movie. When a female is ready to lay her eggs, she stalks her prey – worker fire ants.

A female phorid fly, Pseudacteon sp., hovers over a fire ant worker

Though the flies aren’t venomous, they lay their eggs through a small stinger-like organ on their abdomen called an ovipositor. When the time is right, the female strikes, injecting her egg in the thorax of the worker ant. All of this takes less than a second.

The newly hatched larvae move through the ant’s body into the head, where it happily munches on the ant’s hemolymph (insect blood). This part doesn’t cause much harm to the ant, but once the fly gets ready to pupate, it releases an enzyme that degrades the membranes that hold the ant’s exoskeleton together.

An ant that has been decapitated as a result of Pseudacteon parasitism

While the fly keeps eating the contents of the ant’s head, eventually the head comes loose from the body and pops off.

The fly continues to grow inside of the now disembodied head. A few weeks later, the adult emerges, mates, and (if female) starts the cycle anew.

An adult Pseudacteon litoralis emerges from an ant head

Photos courtesy of UFL.

Releasing Flies to Control Fire Ants

Remember – ant-decapitating flies are parasitoids, and parasitoids are highly host-specific. So releasing ant-decapitating flies is one avenue to controlling fire ants, and something entomologists have been working very hard on.

Entomologists have long observed that populations of a pest insect are always much lower in that pest’s native environment. This is because of the presence of natural enemies (usually parasitoids) that control it. The same is true for fire ants. Fire ants are actually much less abundant in their native ranges of South America than in the United States.

In the mid-90’s scientists began researching and releasing these flies throughout the southeastern US. Today, 6 different species of fly have been released in 11 states in the hope of controlling invasive fire ants.

But before you get all excited about introducing these in your garden, you should know that unfortunately, these flies are not available as a commercial product.

Biological control is a rather unglamorous subfield of entomology because the projects tend to take many years. This might be frustrating if you have fire ants now, but it’s all for the purpose of protecting the overall ecosystem.

It’s dangerous to tamper with the environment by releasing species into an environment where they are not native. In fact, the reason we even have biological control projects today is because many introduced species have gotten out of hand from before we realized the harm of releasing them.

So today, scientists have to proceed with caution and do years of lab-only research before they can get permission to release a new species, even one that attacks a pest exclusively.

How You Can Get Involved

While you cannot purchase any ant-decapitating flies to release in your own yard, if you live in the Southern US and have fire ants, you might consider contacting your local university’s entomology department. If you have fire ants and live in the northeast United States, you probably have European fire ants, which the flies do not attack.

Depending on where you’re located relative to release sites of flies, you may be able to help participate in the research. Biological control projects frequently seek out community volunteers to help monitor populations of insects or to provide sample specimens of host insects to see if they have been successfully parasitized.

Of course, if you are struggling with a severe infestation, you may just need to take care of it. So make sure to check out our guide to getting rid of fire ants to see how to go about it safely and effectively.

Ant-Decapitating Flies FAQ’s

Where are ant-decapitating flies found?

They can be found throughout the Southern United States, since we have native Pseudacteon flies in addition to the biological control ones. The flies that attack the invasive fire ants are native to South America.

How can I recognize the flies?

To be honest, you probably won’t see these flies enough to need to recognize them. They are not yet completely established in the US, and they are tiny and nondescript. Moreover, they aren’t really attracted to anything except for fire ants.
The better way to identify their presence is to look for decapitated ants. There is very little chance of an ant being neatly decapitated by any other creature, so if you see little headless ants around fire ant mounds – that’s a sure sign.

Will the flies hunt any other insects?

Nope! The flies are extremely host-specific. Most species of fly only attack one species of ant, or at most a few closely related species of ant. Don’t worry about the flies attacking any beneficial insects. There is no chance of that happening. That’s what the years of research are for!

Are there ant-decapitating flies native to the US?

Yes! We don’t talk as much about native fire ants because they don’t cause as much trouble for people (though they can cause infestations that require treatment). But we do have them, and we do have flies that attack them. However, the native flies do not attack nonnative ants.

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Written by Miles Martin

Miles is a professional science writer with a Bachelor of Arts in Biology from the University of Rhode Island and a Masters of Science in Science Communication and Public Engagement from the University of Edinburgh.

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  1. So… In an attempt to remember the name of the fly that controls fire ants, I googled it and thought this looks like a good source.😞 Nope, went through whole thing and still wondering, whats the name of that thing?

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