Ant science: Ants try to eat protein beverages like solid food


Collectively, ants are efficient, and you might even call them smart. But individual ants are so dumb that they don’t even know how to feed themselves, as we show in the latest paper to come out of my lab. You could say that these ants have a drinking problem.

A bullet ant with a bubble of sugar solution in its mandibles. Image by Alex Wild

A bullet ant with a bubble of sugar solution in its mandibles. No scale bar is needed; this ant is about the size of your pinky finger, unless you have a small hand. Image by Alex Wild.

If you’re given a protein smoothie, you drink it. But if you give bullet ants a protein drink, they chomp and pull at it. If they knew how to use a fork, they’d probably try that, too.

The bullet ant Paraponera clavata has a boring diet: workers mostly collect sugar water from the rainforest canopy, supplemented with chunky prey items, like other ants and pieces of caterpillars. When they eat carbs, it’s in the form of a liquid which they gather in a droplet held by their mandibles. When they get protein, it’s in the form of a solid which they chomp and bite.

While attempting to do an experiment, we discovered that these ants are absolutely hopeless at drinking a liquid, if it’s a protein solution.

What does it look like when ants try to drink something and when they try to chomp at solid food? Here are two very short videos taken by Jenny Jandt:

We asked: what sensory cues do the ants use to decide whether to drink a fluid or to grasp at it as if it were a solid? We ran a field experiment with factorial combinations of various sugar (sucrose) concentrations and various protein (casein) concentrations, and used ethograms to measure behavioral responses. We replicated this across a bunch of colonies, randomized the order of presentation, and did other good stuff to make sure the experimental design wasn’t messed up. (We’re pros, you know.)

We mostly didn’t get stung while running the experiment. This matters because they are called “bullet ants” for good reason.

We found that the higher the concentration of sugar, the more likely the ants were to drink. If there was a little protein and no sugar at all, the ants would most likely grasp.  Once protein concentrations got near 1 micromolar concentration, however, the concentration of sugar did not affect the grasping response to protein.

So, if these ants are thinking, then this is what they’re thinking to themselves: “If I taste protein, it must be food. So I’ll chomp at it, even though it’s a liquid.” But, it doesn’t look like they’re thinking much at all.

We found that the ants demonstrate a fixed action pattern of feeding behavior in response to assessing the nutritional content of food. This operationally works for them in nature, because texture and nutritional content are coupled. When we experimentally decoupled texture and nutritional content, then we were able to identify the cues that the ants used to make their food handling decision. They decide to drink when they detect carbohydrates and they decide to chomp when they detect protein, and texture has little to do with the decision.

How this project happened in a teaching-centered institution

In the first half of 2011, Hannah Larson (a Master’s student in my lab) was spending several months at La Selva Biological Station in Costa Rica, working with a microbial symbiont of bullet ants. She discovered the phenomenon of bullet ants chomping at protein solutions when she tried to experimentally feed colonies a protein solution, and the colonies opted to dismember the plastic pipets instead of drinking from them. She worked out other ways of delivering protein for her experiments, but we wanted to document and further understand this discovery.

That summer, I paired up my colleague Dr. Jenny Jandt up to mentor a student from my university on a totally different project. We all found this protein-chomping behavior so cool, and Jenny made the time for a second trip to Costa Rica after I helped her flesh the project out. My undergrad Peter Tellez was her wingman, and they did the experiment using the template of the many colonies that Hannah established for her thesis work. In late 2011, I drove out to visit Jenny in Tucson for a couple days, to work on this and another manuscript, in which the bulk of the paper was put together. Jenny put the finishing touches on this paper with just a bit of help from myself, Hannah and Peter. As it was a side project for all of us, it lingered a bit but Jenny persisted and she’s pretty much everything I could ask for in a collaborator and mentor to our students.

Where are they now? Jenny took a postdoc in the rockin’ lab of Amy Toth at Iowa State. Hannah is now in her second year of the DPT program at the Univ. of Washington and Peter is now a PhD student in the lab of Sunshine Van Bael at Tulane.)

In short, this cool paper came together because I was able to talk my postdoc buddy Jenny into coming down to the rainforest to work with my students for about a month. She is otherwise a wasp and bee behavior person, and I was glad to give her an avenue to work with ants and tropical rainforests, and my students greatly benefited from her careful mentorship and expertise in individual and collective behaviors of social insect colonies.

Reference: Jandt, J., H.K. Larson, P. Tellez, and T.P. McGlynn 2013. To drink or grasp? How bullet ants (Paraponera clavata) differentiate between sugars and proteins in liquids. Naturwissenschaften. DOI: 10.1007/s00114-013-1109-3

A copy of this paper is available on my lab website here.

This work was conducted under support of the National Science Foundation (OISE-0854259 and OISE-1130156).

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