New studies suggest that different butterfly species utilize sound to hide from ants so that they can devour young ant pupa or trick the ant workers into serving them like queens. Research into the mechanism by which butterflies can trick ants into giving them queen-like treatment or into becoming easily-devoured prey raises questions about how insects communicate with each other, in addition to providing a truly curious case of coevolution.
For over 30 years, researchers have been fascinated with butterflies from the genus Maculinea and their strange life cycles. The life cycle begins when an adult female butterfly lays her fertilized eggs on or in plant. There, the larvae hatch and feed on flower parts until they become big enough to drop to the ground. Thus far the larvae are considered to have lived their entire lives in the “pre-adoption phase” of their life cycle. They transition to the “post-adoption phase” of their development when passing Myrmica ants pick up the larvae and bring them to the brooding chambers in the ant colony. There, the caterpillars will live for 11 to 23 months by using one of two feeding strategies. “Predatory species”, such as M. teleius and M. arion will devour the still-developing ant pupa. “Cuckoo feeders” such as those from M. alcon and M. rebeli will recruit worker ants to feed them.
Both cuckoo feeders and predatory feeders are clearly parasites on the ant colony. In both cases, the ants fail to recognize the parasites and instead allow them to live within their nests. The questions that this phenomenon raised about how ants can communicate and how they can be so easily duped into not recognizing such an obvious threat intrigued researchers to find out more.
Previous research has clearly demonstrated that a large part of ant communication is done using chemicals. Indeed, examination into the behavior of some of the cuckoo feeding species of Maculinea showed that the adopted caterpillars emitted chemical identifiers that mimicked those produced by their parasitized ant hosts.
However recent research has highlighted the importance of audible communication used by ants. Though not as essential as communication by chemical signaling, acoustic communication has been demonstrated as a key component of some parts of ant communication—particularly for identifying queen ants.
Researchers hypothesized that perhaps part of the Maculinea butterflies’ success in being adopted into a nest might also be attributable to adaptions that allow it to mimic the sounds of the ants that they parasitize. Indeed, upon recording the sounds made by both ants and caterpillars using sensitive microphones, it was shown that Maculinea caterpillars do in fact mimic the cries of ants. This could quite possibly by a key factor in how ants are lured into adopting the caterpillars and brining them back to live in the brooding chambers of the ant colonies.
In addition, it was also found that among cuckoo feeding butterfly species, the caterpillars were able to use vocalizations to mimic the cries of ant queens. The cuckoo feeding strategy dictates that they must closely mimic the developing ants with which they share the brooding chambers. As such, the caterpillars must compete with the ant pupae to get food. In the event of a food shortage in the ant colony, it is possible that some of the young ants or the caterpillar will starve. To reduce this risk and horde as many resources as possible for itself, caterpillars from the genus M. alcon use sounds to mimic queen ants. Because queens have a higher social status in ant colonies, the parasitic caterpillar is insured extra food rations are delivered the serving worker ants.
Along with Maculinea butterflies is estimated that there are 10,000 species of arthropods that socially parasitize ants. Therefore it is possible that further studies into acoustic communication by parasitic butterflies may yet reveal that other species also use this trick to fool ants into serving them as queens and/or devouring young ants as easy prey.
By Sarah Takushi