Structural Pests: A Conversation with Asim Renyard

 

Debbie Chan— On the topic of communication, can you tell us about how carpenter ants use pheromones and vibrations?

 

Asim Renyard — Pheromones are useful because they can be dispersed through the air, and they can be followed by others. When an ant emits a pheromone, it will linger in the air and form little plumes, like plumes of smoke. Because these linger, they don’t give very timely information, whereas with vibrations it’s more instantaneous. Carpenter ants will drum their body against the ground to send out a vibration in 360 degrees, which other ants can sense. But here, they have to consider their substrate. If they were to vibrate on dirt, the transmissibility would be very poor, but if they drum onto wood—where they build their homes—that signal will transmit very far, so ants select which communication method will best suit their situation.

 

Sena Cleave — What does it look like when carpenter ants drum their bodies against the ground? 

 

AR — They’re positioned horizontally on all six legs, and they raise up, like the ant equivalent of standing on their tippy toes, and then they smack their whole body against the ground…

 

DC — Very fast?

 

AR — Yeah, we record it in our lab with a high-speed camera. With the naked eye, it just looks like they’re vibrating, but under the slowed footage you can see a very distinct, up and down, smacking motion. 

 

DC — Like doing squats?

 

AR — Haha! Yeah, and they do a couple different types, too. Sometimes they’ll whack just their butt against the ground, and other times they’ll do something like a heavy metal headbang, where they’ll rear their head up and swing it back down. 

 

SC — With all these different techniques, do carpenter ants ever miscommunicate?

 

AR — In the sense that the ant receiving a signal misinterprets it? 

 

SC — Yeah, or I was thinking about how ants leave plumes of pheromones in the air. Can those signals then move, and then draw an ant to the wrong place? 

 

DC — Can it mix with other scents, maybe?

 

AR — I’d certainly say, in the way I’ve been describing it, it sounds like ants are incredibly sophisticated creatures that don’t make any errors. And, as a group, ants can do phenomenal tasks, but each individual is not that capable. Say, if an ant puts down a trail of pheromones, not all ants are going to follow it. And they may lose their way, or they may decide… well, decide... it’s hard to say if the ants are deciding the way humans do. But they certainly don’t all coordinate perfectly. Sometimes I’ll go feed insects to one of the ant nests we have in the Lab, and I’ll see one ant on one side of the insect, with another ant on the other side, and they’ll both be pulling it in opposite directions.

 

What leads to a colony's incredible, collective efforts is when most ants decide to do it one way, so there forms a consensus, and they all will respond in that way. 

 

SC — That brings me to the labor of homebuilding, and it seems like the biggest misconception about carpenter ants is that they eat wood. 

 

AR — Carpenter ants excavate wood with their mandibles, which are their pointy mouth parts. They make these elaborate systems of tunnels and galleries to form their homes, and the wood they chew will be dumped outside.

 

SC — When they're homebuilding in the forest, say in a tree that is alive, is there a chance that they will eventually kill it?

 

AR — It’s hard to say. Typically they excavate into the heartwood of the tree which, I think, is no longer actively growing. 

 

DC — So they’re not parasitic?

 

AR — No, probably what's more detrimental is that once carpenter ants are in a tree, they attract predators like woodpeckers, who will bore into the tree trunk. 

 

SC — What about when they chew into buildings, can they destroy a whole infrastructure? 

 

AR — Not really, usually people catch it in time. But they can be a significant structural pest. It’s rare, but, if no one intervenes, they will weaken a building enough that it can collapse. I think there have been reports where the roofs of people’s cabins will cave in because carpenter ants have chewed through the beams. 

 

DC — This makes me wonder about the relationships between carpenter ants and other parts of their environments. Can you speak to the idea of an ecological niche, and where the carpenter ant fits in?

 

AR — I would say an ecological niche is a collection of all of the interactions an organism has with its environment, both with living aspects and non-living aspects. There’s a give and take, back and forth between an organism and its surroundings. 

 

Ants are known to have many relationships with other species, so much so that many types of ants are considered ecosystem engineers. They’re often a dominant force of change and can transform both the biological and the physical conditions of their environments. That being said, for the carpenter ant, the ecological roles are not very well studied. We have an idea about the kinds of relationships they have—they farm aphids, break down wood, prey on insects, and act as food for larger creatures, for example—but we don’t know the scale of their impact. We’re not yet certain about the extent to which these roles are changing the ecosystem.