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When studying insects deep in the Peruvian Amazon, sometimes all you can say is “wait- this is weird, right?”
That was my expert opinion – “weird” – that I declared to our TechKnow producer and production crew while watching this obscure group of insects known as barklice (not related to head lice) move in almost perfect coordination.
At first I couldn’t put a finger on why this six-legged dance looked so odd- until I realized that when one moves, so do the others, and when one pauses, so do the others- but all in different directions. It’s a cohesive, start-and-stop movement that I haven’t seen before in any animal.
So I wondered, had anyone documented this before? The answer, it appears, is no.
How does a one millimeter insect inches away from another know when to start and stop? And why pause in coordination when they could get to their destination faster if they just kept walking?
My first guess for the how was that they could ‘feel’ each other’s movements through the silk they live within; other animals like spiders are known to send messages through vibrations in silk so why not barklice too?
Back from the remote rainforest and into civilization, I tried searching through scientific literature for anyone else who had seen this. Nothing. It was time to call in the experts to get to the bottom of this.
I started with Dr. Alfonso N. García Aldrete, researcher at the Universidad Nacional Autonomo de Mexico who has published extensively on this group in Latin America. His thoughts? “No idea about that behavior,” but he did help me identify this group as the genus Archipsocus.
Next up, Dr. Glauco Machado of Universidad de Sao Paulo in Brazil, neighboring Peru. Again, hadn’t seen this before, but did guess that it could be an altruistic behavior and by moving together a predator could “perhaps mistake the whole aggregation for a single organism.”
So the people that work with this group hadn’t seen this type of movement, but what about in other groups of animals- could there be fish or birds that move like this, or maybe this movement an entirely new thing.
Enter Dr. Iain Couzin, arguably the world’s top expert in cohesive animal behavior who has a lab at Princeton and recently moved to be the Director of the Department of Collective Behavior at the Max Planck Institute for Ornithology in Germany.
Couzin studies “how animals coordinate their motion and make collective decisions regarding when, and where, to move” and works with species ranging from “swarming locusts to schooling fish and even human crowds.”
So if anyone were to have heard of a start-stop, mass movement like the barklice do, it would be Couzin.
But he hadn’t, and he was amazed. “In all honesty I don’t know why they would move like this,” he told me, but wagered what seems an excellent guess. Some species are known to stop in order to detect predators around them. It’s hard to hear a predator if you’re making noise, or detect their movement if you’re moving yourself. “So the group may be going through a repeated process of move together - check for external cues - move together, and so on.”
“There seems to be evidence of rapid social transmission across the group allowing them to behave almost as a single entity. My other thought, of course, was ‘wouldn’t this be fantastic to study - where can I find some?’” Both he and his grad students are eager to get to the bottom of this, and watching their discussions on potential mechanisms and origins of the behavior unfold over email even further fascinated me.
Just when I thought the mystery was undocumented and had a solid hypothesis to go on, I reached out to one more researcher, Dr. Edward Mockford of Illinois State University. He has spent his career looking at the evolutionary relationships of barklice, finding many new species along the way.
Mockford has “observed this coordinated behavior many times” back in the early 1950s And there we have it. However, he never was able to record it or in fact realized that is may be so unique to barklice. He admitted “I haven't thought much about its function, but I suspect it has to do with directing energy to where the most attention needs to be placed for repair and maintenance of the web.”
Another researcher, another hypothesis, this time possibly to direct movement towards repairing the web that makes their communal home.
What fascinates me in this case is that as specific as a group as barklice in the tropics may be, different scientists I talked to had completely observations that stand out and different questions resulting. While Couzin and I wondered “how do the move like that?” Mockford immediately wanted to know “what species is that?”.
One thing is for sure; the barklice mystery doesn’t end here, especially with these scientists involved. Couzin has requested better video footage from a tripod the next time I’m in the field for them to analyze, and Mockford has requested I collect specimens so he can identify them and see if they are a new species.
One simple video of a odd insect movement, a lot of questions to be answered. To make matters more interesting, I also found this video of a similar barklice behavior, this time with no silk.