Zombie Ants

How do you make a group of master gardeners and budding entomologists cheer? Show them a video loop of the phorid fly stinging a fire ant and laying its egg in the insect.

How do you make that group roar with excitement? Show the part of the video where the ant's head falls off.

Almost every speaker this week has shown us that video, and it has never failed to elicit that response. (Unfortunately, it's a National Geographic video available for educational purposes, and my blog isn't yet considered educational. If you google it enough, you might find it, but I am way too tired to do that.)

But you know what is even better? Watching the decapitation in person!

Today we visited UT's Brackenridge Field Laboratory on Lake Austin Boulevard to see where this amazing project takes place, and I was just absolutely fascinated.

You can read more about it here and here, but I'll also share my observations.

I grew up in Mobile, Alabama, which is famous (or infamous as the case may be) for two main things: celebrating the original Mardi Gras in the United States (having gone to college in New Orleans, I know that the New Orleanians are going to want to fight you on this one, but hold your ground, or at least bet a few drinks before you show them they are wrong), and being the port of entry into the United States for invasive fire ants in the early 1900s. (Hmm, I wonder why the City of Mobile website doesn't mention that factoid?)

Growing up, I had no idea that these biting, pustule-forming pests weren't everywhere. The invasive ants were imported accidentally from Brazil and Argentina, as ballasts in ships returning from South America. I certainly had no idea that they caused $6 billion worth of damage annually, $1.2 billion in Texas alone, that they can attack and kill ground and tree-nesting birds and animals, or that they had spread throughout Europe, creating one supercolony expanding from Italy though France into Spain.

Okay, okay, enough of the history, on to the decapitation. The invasive fire ants thrive and spread here in part because they have no natural predators. Scientists figured out that native phorid flies keep the populations in check in Brazil and Argentina. The flies, which are far smaller than the ants, terrorize the ants, who literally cringe in fear. The flies sting the ants, depositing eggs into the ants' abdomens. This whole process takes 1/30th of a second, and the fly can repeat it between 100 and 200 times.

The stung ant retreats into the mound, where the egg grows inside the ant and metamorphizes. As the fly reaches its last instar, it heads into well, the head of the ant. The fly larva eats the ant's brain and muscle tissue, creating a zombie ant. The ant is still alive but the fly instar is controlling it. The fly turns on the ant's drive switch and gets the ant (now the fly's vehicle) to travel out of the mound, which is an unsafe place for the fly to hatch. Once the ant has reached a good place for the fly to emerge--sometimes 10 to 15 feet away, the fly bursts out of the ant's head. At the same time, the ant's head falls off.

Scientist at Brackenridge now import multiple species of these flies, let them have at ants carefully selected for size (some fly species like the big ants, others the smaller ones) in the Mass Attack room, and then guard these zombie ants for about two weeks until the flies explode out of their heads. (Have I mentioned that part yet? About the fire ants losing their heads?) Sometimes the scientists make controlled releases of these flies to combat the fire ants. Other times the new flies are sent into the Mass Attack room to do what they were born to do.

I hope you've gotten the general idea, and when I've got more time, I'll discuss the differences between the invasive and native species of fire ants. (In Austin, if your house was built before 1980, you probably have native fire ants; if you live in a newer house, you probably have the invasives.)

I certainly never thought I would find fire ants and flies so fascinating!