Phil and I both have backgrounds in entomology, and yet we had never seen anything like this before. Sure, we knew that some butterfly larvae have symbiotic relationships with ants, known as myrmecophily. This is well documented -- many of the caterpillars that associate with ants have special organs that secrete sugars and amino acids. The ants get a sugary nutritious meal from the caterpillars and, in return, the fragile caterpillars get personal ant bodyguards that defend against predators and parasites. But this is not the case for the adult butterflies, which usually have to evade ants lest they become their next meal.
"Look at the three red spots on the butterfly wing." Phil said. "Kind of looks like the ants they're with on the bamboo. Maybe it's some sort of mimicry." Now I was really interested. The butterfly appears to be a known species,Adelotypa annulifera, but these pictures could be revealing an undocumented observation for this butterfly interacting with ants and a potentially new wing-mimicry pattern. Super cool, I thought, but there was just one problem: we know little about this butterfly beyond some dead pinned specimens. What is its life cycle? Where do the larvae develop? What do the larvae even look like? Next to nothing was known about the life history of this butterfly. So to solve this mystery, Phil and I decided to collaborate. I was making a return trip to this exact field site in the coming months, so I set out to uncover the missing pieces of this puzzle.
The challenge with this type of fieldwork is that the Amazon rainforest is huge, and the critters we are looking for are tiny. Since Phil observed the butterflies on bamboo, I ventured out to the same habitat, a trek from the Tambopata Research Center. The jungle was particularly hot, humid, rainy and muddy during that expedition, but I was determined to find our caterpillars and butterflies. After hours of hiking through the Peruvian Amazon and getting soaked by the rain, I found myself in the bamboo forest where we knew our butterflies liked to hang out. I checked dozens of bamboo plants but it seemed futile -- no signs of our butterflies. But persistence is the key to fieldwork. I soon saw a young bamboo shoot poking out of the mud, and noticed a leaf near the base of the bamboo, close to the ground.
I pulled the leaf back and to my utter shock, found myself staring directly at two caterpillars nestled against the bamboo and an agitated ant hovering over the Lepidoptera larvae. My heart was pounding -- did I really just find our caterpillars in this vast rainforest!? Clearly they were myrmecophilous, as the ant was trying to protect them.
Although excited about the find, I knew the job wasn't done. This could be any species of caterpillar, so I knew I had to watch them turn into pupae and then adults in order to confirm that these belonged to the same butterfly species. I checked up on the caterpillars at that spot and took photos and video. After a couple of days, I found our little critters in the same location, but this time they had transformed into pupae! I gently collected them and brought them to a small insect cage at the Tambopata Research Center to see if they would emerge as butterflies. I had my fingers crossed; hopefully they would survive to adulthood.
Days later, I walked past the little insect cage and noticed some activity. Wings fluttering. One of the pupae had successfully eclosed! It was the moment of truth -- what butterfly was it? My jaw dropped when I noticed it was, in fact, the same butterfly (Adelotypa annulifera) that Phil had taken pictures. That means we had just completed the entire life cycle of the butterfly, from egg to larvae to pupae and finally adult. Now felt like we had enough material to write this up as an official scientific publication.
We think the fact that butterflies steal a resource from the ants and let the ants crawl all over them indicates that some complex chemical signaling is going on. Perhaps the butterflies are utilizing a pheromone from their larval stage, potentially allowing the butterfly to take advantage of the ants, which would normally tear a fragile butterfly to shreds. The three red spots on the butterfly wing also look strikingly like the red ants and perhaps serve as a form of mimicry. If a butterfly looks like red ants that bite and sting, a bird may be less inclined to eat it. However, it should be noted that these are just our hypotheses at the moment and, like any hypothesis, should be rigorously tested before we can claim to back it up. We hope to do so, because there most certainly seems to be more to this incredible tropical butterfly than meets the eyes. Stay tuned.
For more info, you can download the PDF here. One more fun fact: it was actually during this trip that I accidentally discovered a totally new, yet unrelated, butterfly-ant relationship. The jungle is full of endless surprises.