A dragonfly on a path at Xandari

Whenever I have the opportunity to visit a national park in Costa Rica, I obviously take my camera with me so I can try to get some good photos or videos of all the wildlife I hope to see. Looking back on my files of images from the past couple months, I realized that I happened to have some half-decent videos that represented what I’d consider the four most important classes of Kingdom Animalia/Metazoa from the point of view of a terrestrial biophile: Aves, Reptilia, Mammalia, and Insecta. In other words, when I’m walking through the rainforest, the animals I keep an eye out for will likely fall into the category of bird, reptile, mammal, or insect. If I’m out at night, then maybe Amphibia will get thrown in there too!

In the video above, you can 

see a male Yellow-headed Gecko waving his tail territorially, a male Blue-crowned Manakin singing to attract a mate or claim a little plot of forest, a pair of Nine-banded Armadillos foraging in the leaf litter, and a horde of caterpillars (most likely the larvae of the Banded Peacock Butterfly commonly seen at Xandari) moving in a bizarrely efficient way across a footpath. All the animals were seen at Carara National Park except these last caterpillars.

Of all the animal behavior displayed in the video, the most weird — and most creepy or disconcerting, for most people unless they’re geckophobic — is that of the caterpillar treadmill. Why would the group of crawlers decide to writhe all together, moving slowly along a forest path where they are so easily seen and can be picked off? Our first answer might draw from our experience with the herd or school instinct, where zebras or fish move in packs to stay safe in numbers: even if a predator comes along and snags a straggler or two, the majority of the animals will get away. But I searched around, and found that Destin Sandlin, from Smarter Every Day, has come up with a cleverly illustrated explanation for the phenomenon, using nothing other than Lego and a little math! Rather than repeat what he has already so well elucidated, I’ll throw in his video reasoning below.