S A N F R A N C I S C O, Jan. 10, 2001 -- A colony of cannibalisticants discovered in Madagascar represent an important piece of thepuzzle in understanding the evolution and behavior of one of themost successful insect species in the world, scientists saidtoday.
The fearsome-looking insects, dubbed “Dracula ants” by theirdiscoverers because they suck nourishment from their own larvae,are believed to be a transitional species bridging the gapbetween ants and the wasps from which they evolved millions ofyears ago.
“A living organism cannot be a true missing link,” said BrianFisher of the California Academy of Sciences, who found the antcolony hidden in a rotten log about 55 miles outside ofthe capital Antananarivo.
“But this represents our best hope for understanding what thecommon ancestor was, which has been a huge impediment forunderstanding ant evolution.”
While ants make up only about one percent of all describedinsect species, they are among the most widely spread andnumerically dominant on Earth — and researchers want tounderstand the evolutionary secret to their success.
Ants Have Wasp Waist
Madagascar, an island off southeastern Africa, is regarded asa treasure trove of biological information because its relativeisolation allowed older, or “relic,” species to survive withoutcompetition from newer arrivals.
While the genus of the “Dracula” species was first identifiedin Madagascar in 1993, Fisher’s discovery of the first entirecolony of the insects allows scientists to draw a more detailedpicture of ant evolution.
The Madagascar ants, belonging to the genus Adetomyrma, havejust a single connection between their thorax and their abdomeninstead of the two or three joints found in “modern” ant species,Fisher said.
“They have got this wasp waist, if you will,” he said, addingthat the single joint was a clear indication of the ants’ link toearlier wasps.
The Adetomyrma ants also display a grisly feeding habit whichFisher 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 nurseryand cut holes into their own larvae to feed on the hemolymph, theequivalent of insect blood.
“They chew them until they bleed,” Fisher said, explaininghis 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 thepractice of other ant species in which worker ants, which areunable to digest solid food themselves, feed the larvae, whichregurgitate part of the digested food back to the workers fordistribution around the colony.
Fisher said further study of the “Dracula” colony couldprovide more clues on the development of ant behavior — andcould eventually force scientists to rethink their entirehypothesis of ant evolution.
“This initial discovery told us that our current hypothesisof the evolution of ants was inaccurate,” Fisher said. “It is notjust important in that it is a new species...it is an importantpiece of the puzzle in the evolution of life.”