A colony of cannibalistic ants discovered in Madagascar represent an important piece of the puzzle in understanding the evolution and behavior of one of the most successful insect species in the world, scientists said today.
The fearsome-looking insects, dubbed “Dracula ants” by their discoverers because they suck nourishment from their own larvae, are believed to be a transitional species bridging the gap between ants and the wasps from which they evolved millions of years ago.
“A living organism cannot be a true missing link,” said Brian Fisher of the California Academy of Sciences, who found the ant colony hidden in a rotten log about 55 miles outside of the capital Antananarivo.
“But this represents our best hope for understanding what the common ancestor was, which has been a huge impediment for understanding ant evolution.”
While ants make up only about one percent of all described insect species, they are among the most widely spread and numerically dominant on Earth — and researchers want to understand the evolutionary secret to their success.
Ants Have Wasp Waist
Madagascar, an island off southeastern Africa, is regarded as a treasure trove of biological information because its relative isolation allowed older, or “relic,” species to survive without competition from newer arrivals.
While the genus of the “Dracula” species was first identified in Madagascar in 1993, Fisher’s discovery of the first entire colony of the insects allows scientists to draw a more detailed picture of ant evolution.
The Madagascar ants, belonging to the genus Adetomyrma, have just a single connection between their thorax and their abdomen instead of the two or three joints found in “modern” ant species, Fisher said.
“They have got this wasp waist, if you will,” he said, adding that the single joint was a clear indication of the ants’ link to earlier wasps.
The Adetomyrma ants also display a grisly feeding habit which Fisher believes may be the basis for the “social food sharing” that has come to characterize ant colonies.
Queens Cut Holes in Larvae
Queen and worker ants, when hungry, visit the colony nursery and cut holes into their own larvae to feed on the hemolymph, the equivalent of insect blood.
“They chew them until they bleed,” Fisher said, explaining his decision to dub the genus after the vampire Dracula of lore. “We call this nondestructive cannibalism.”
Fisher believes that this practice may have evolved into the practice of other ant species in which worker ants, which are unable to digest solid food themselves, feed the larvae, which regurgitate part of the digested food back to the workers for distribution around the colony.
Fisher said further study of the “Dracula” colony could provide more clues on the development of ant behavior — and could eventually force scientists to rethink their entire hypothesis of ant evolution.
“This initial discovery told us that our current hypothesis of the evolution of ants was inaccurate,” Fisher said. “It is not just important in that it is a new species...it is an important piece of the puzzle in the evolution of life.”