February 05, 2009
The Western European butterfly Maculinea rebeli lives off ants in its early life stages. The ant species Myrmica schencki carries the butterfly larvae to its lair, believing that the larvae is its own. Once inside the butterfly larvae are able to deliver the same chemicals as ant larvae which cause the ant workers to feed the butterfly larvae themselves, providing its food needs until 11 to 23 months later when the butterflies pupate.
However, the researchers were perplexed when they observed that the butterfly larvae received more than the basics, time and again they observed the butterfly larvae receiving preferential treatment. “[Butterfly] larvae are rescued in preference to ant larvae when a colony is disturbed,” the scientists write, “furthermore, nurse workers kill and feed their own brood to the social parasite if food is scarce”. This behavior extends to the ant’s queens: “we even observed [ant] queens treat [butterfly] larvae or pupae like rivals, whereas the workers regularly treat them like royalty”.
While ant vocalizations had not been as widely studied as their chemical communications, the researchers believed this might hold the key to the butterfly’s success. They recorded the vocalizations of both the ant workers and the queens, and discovered significant differences in the queens’ “dominant frequency and overall acoustics”. When the queen’s vocalizations were replayed, worker ants would gather around the caller and guard it. The researchers found that this was “consistent with the exalted status and protection afforded to queens in the hierarchy of a colony”.
Researchers then turned to the parasitical butterfly larvae, whose vocalizations were mimics of their hosts’. However, the scientists discovered that the sounds were 23 to 27 percent closer to the queens’ over the workers’, thus providing them with first-class treatment. While the butterfly larvae may use chemical resemblance to infiltrate the colony, once inside the colony it is the mimicked vocalizations that allow it to rise to the top, often at the expense of its hosts’ offspring.
The butterfly Maculinea rebeli is not the only insect to survive off ants. Scientists believe that ants are prey to about 10,000 different social parasite species. The new research suggests that mimicking vocalization may play a much larger role in duping ants than originally believed.
CITATION: Francesca Barbero, Jeremy A Thomas, Simona Bonelli, Emilio Balletto, Karsten Schönrogge3 (2009) Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite. Science Magazine, Volume 323.
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