Destin, of smartereveryday, and Phil Torres, conservation biologist, managed to spot and record these social caterpillars (?hymenopteran Perreyia sp) moving on the rainforest floor of the Amazon. The group behaviour of social caterpillars is thought to give them an advantage in a variety of ways such as in foraging, predator defence, thermoregulation, and shelter construction. However, Destin and Phil noticed that these 'caterpillars' (actually sawfly larvae) were moving as a group in a particular fashion. Besides moving as a collective, generally the larvae at the rear would climb on to the ones in front of it, and continue walking over its siblings if there are any beneath it. This behaviour (mass locomotion) is almost rolling or as Destin describes, "kinda like a wheel".
As the larvae on top will be moving at a greater relative speed, Destin hypothesises that this form of group locomotion gives the collective a greater speed of travel versus a single layer of larvae (or an individual larva). To test this out, he modelled the behaviour using his son's Legos.
Catching the attention of Aatish Bhatia, at EmpiricalZeal, Aatish further examined the video using Tracker, a video analysis and physics education program.
Tracking the motion of the larvae and with some mathematics, he confirmed that:
By working together, these caterpillars can move twice as fast as they would by themselves! This is probably why they crawl over each other in this rolling swarm.
Aatish and commenters to his article are continuing to derive the formula to calculate the "speed of N layers of caterpillars" so do check it out to see how they progress.
Swarming/self-organising behaviour is of great interest to AI and robotics researchers.
It would be fascinating (and awesome) to model this locomotive behaviour robotically. I haven't come across any swarming robotics that do this yet. If you've seen something like it, let me know :D
Update: More videos of Perreyia sp moving en masse.