Entomologist Aaron Pomerantz was walking through the Peruvian Amazon rain forest recently when he noticed something odd: a bunch of yellow growths on the side of a tree. They didn’t look like any fungi he’d ever seen, and he couldn’t immediately identify what they were. Looking closer, he saw a furry-looking caterpillar munching on the yellow buds. And these caterpillars, in turn, were being tended to by ants, which appeared to be protecting them from predators. Pomerantz also noticed an ant stroking the caterpillar until it released a bead of liquid food from its back, which the ant greedily slurped up.
Lastly, he saw butterflies hanging out around the buds. The wings boast colorful spots, which are exactly the same yellow hue as the buds, says Pomerantz, who works with Peru’s Tambopata Research Center.
After doing some research, Pomerantz found that nothing like this had ever been documented. For one, the yellow growths belong to a "very unusual and rarely seen" parasitic plant belonging to the family Apodanthaceae. Secondly, he identified the butterfly as the species Terenthina terentia, which was already described, though nobody knew what its larval form—the bud-eating caterpillar—looked like. The yellow spots on the adult's’ wings may help it blend in amongst the parasitic plant and hide from predators.
He also demonstrated the symbiotic nature of relationship between the ants and the caterpillars, a rare association called myrmecophily. The ants provide protection, and in return the caterpillars produce a nutritious fluid.
Many questions remain, though. How do the caterpillars find the parasitic plants? The buds can only be found from October to January and then fall off. Do the insects eat anything besides these plants? And how do the ants know that the caterpillars will produce food for them, in return for protection? The answers will likely have to wait—until the buds reappear next October.