Sheila Patek: The breakneck world of ants that bite fast and jump high
From left, clockwise: Andy Suarez, Joe Baio, Brian Fisher and Sheila Patek.
UCMP curator and professor Sheila Patek hadn't worked with ants at all — that is, until she received a FedEx box full of them in the mail in the fall of 2004. That package marked both her introduction to myrmecology and the beginning of an investigation destined to make it into the Guinness Book of World Records and the Proceedings of the National Academy of Sciences.
The FedEx contained Costa Rican trap-jaw ants, Odontomachus bauri, a species with extra-long mandibles familiar to Andy Suarez, University of Illinois professor, ant expert, and postdoctoral colleague of Sheila's. When they were both postdocs, Andy tipped Sheila off to the improbably high speeds of O. bauri's jaws, which snap shut on prey and nest intruders. Since she was already working out the mechanics of super-fast appendages in the animal world (of the former world record holder, the mantis shrimp), Sheila was equipped with the high-speed cameras necessary to time the ant's jaws.
"That part of the project was pretty straightforward," says Sheila. She got the ants, figured out how to handle them, mounted them under a microscope with the camera on top, and filmed their jaws snapping shut. She and lab manager Joe Baio analyzed the footage (see below) and found that they were moving at amazing speeds. Andy had been right. Though weighing in at less than 15 milligrams, O. bauri boasts the fastest self-powered predatory appendages yet documented: 145 miles per hour!
Odontomachus bauri, poised to strike
This movie, of the trap-jaw ant's mandibles snapping shut, is 1,667 times slower than real time
While writing up that result for publication, Sheila began investigating the "ant literature" — scientific articles from the late 1800s and early 1900s — which contained a tantalizing suggestion: O. bauri had been observed flinging themselves into the air to escape threats, and some naturalists suspected that that they might be using their jaws to power those jumps. Of course, the ants are so fast that, back then, no one could be sure that they were using their jaws to jump. Sheila's curiosity was piqued: "I thought, 'Wow, that's really interesting.' So I went back to our original data." With those data and some basic physics, she calculated how much force the ants were generating with their mandibles. Once she got those estimates, she realized, "Wow, the ants really could be jumping with their jaws — since they are generating over 300 times their body weight with each mandible! So I called up Andy and said, 'You know, probably this side of it is more interesting...'"
Andy Suarez and Brian Fisher (California Academy of Sciences ant expert and source of the original FedEx) had both experienced O. bauri's jumps up close and way too personal. When a large intruder (like a field biologist) stumbles onto the ants' nest, it triggers a "popcorn" effect: multiple ants fling themselves into the air. Perhaps accidentally, some of them land on the intruder and proceed to inflict painful stings. These jumps directly into the air are called "escape jumps," but the ants also deploy another tactic, called the "bouncer defense," in which they attack an invader with a strike, while simultaneously flinging themselves away.
Though Sheila, Joe, Andy, and Brian had begun with a simple question (How fast are they moving?), now they had a specific hypothesis. They suspected that the ants were using their jaws to jump and that they were intentionally doing so — not just misfiring as had been debated in the literature. So the team set up cameras to capture exactly what happened during an ant's jump.
"When we first got the videos, Brian — who has discovered hundreds of species of ants and knows everything there is to know about ants — was jumping up and down because it was so surprising and exciting to see what they were doing. We all were so excited! We were grabbing people from the hall to come see these videos," raves Sheila. They were watching something that no one had ever been able to see before — and it was quite clear from the film: "For the escape jump, it's definitely intentional. The ants are setting up a jump with their jaws — definitely not an accident." The results of the investigation supported their hypothesis.
The above movie, of the trap-jaw ant "bouncer defense", is 100 times slower than real time.
The above movie, of the trap-jaw ant "escape jump", is 100 times slower than real time.
Sheila didn't begin this project with the goal of demystifying O. bauri's escape jumps. Says Sheila, "I didn't really have an expectation. I just got Andy and everybody here, because I knew this was something interesting and I wanted to understand how these jaws could possibly be used for something other than feeding. There's not a lot of precedent for jaws being used for locomotion — in fact, I can't think of any. I think we all just got together because we were curious and it just seemed like there would be something interesting there." And indeed there was.
And now, there are more questions to answer. It's easy to assume that escape jumps and the bouncer defense are adaptations for nest defense and survival — but according to Sheila, that's a big assumption that actually needs to be tested experimentally: "You can see some really high-performance, cool behavior and not actually be sure whether it's adaptive and whether it's on purpose. With the ants, the truth is that if you are generating that much force to squash things, one accidental consequence is that if you fire against something bigger than you are, you're going to go backwards — whether you wanted to or not. We often assume that the 'designs' we see in nature must be perfect — and they're not. Probably the ants are just messing up sometimes...It's really hard to show if a behavior is conveying a benefit of any kind." The next steps, which are already in the works, involve doing behavioral experiments to determine when the ants perform which jump and whether they gain any advantage (like protecting the colony better or escaping with their lives) by performing a jump. Ultimately, Sheila and her colleagues want to learn about the macroevolutionary patterns of the trap-jaw — how and why the components of the trap-jaw were assembled over evolutionary time. But that is a long term project. Says Sheila, "This is the first paper we've ever written on the topic. There's years and years more work to do to understand the behavior." So stay tuned!
Dig deeper
To learn more about Sheila's research on this topic, see these related resources:
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Patek, S. N., Baio, J. E., Fisher, B. L., and Suarez, A. V. 2006. Multifunctionality and mechanical origins: Ballistic jaw propulsion in trap-jaw ants. Proceedings of the National Academy of Sciences 103(34):12787-12792.
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Discover the evolutionary story behind the amazing feats of the trap-jaw ants, along with links to handy background information, in Quick bites and quirky adaptations.
