杏吧原创

Army ants infamously visit destruction upon thousands of unlucky insects, but new findings highlight one of the ways the insects bolster biodiversity as well. The hodgepodge collections of food waste left behind by raiding army ants serve as nurseries for numerous beetle species.

Army ants (many of which are in the Eciton genus) forage in mass raids, where a tsunami of clattering pincers pours along the ground. Insects and other arthropods caught up in the tide are killed and consumed back at the 鈥渂ivouac鈥�, a dense ball of living ants that serves as a temporary nest. There, prey fragments and dead army ant workers accumulate, and so when the army moves on it leaves behind a loose jumble of severed legs and shattered heads roughly the width of a dinner plate.

Since the 1960s, these middens have been recognised as a jackpot for scavenging insects. But most of the research into army ants鈥� impacts on other species focused on their prey, birds that follow raids to eat spooked insects and symbiotic species living within the colonies, says at the Rockefeller University in New York City.

鈥淗ardly any work had been conducted on the many insects that visit army ant refuse deposits,鈥� he says.

Kronauer, working with at the Technical University of Darmstadt in Germany and an international team of researchers, started investigating. Together they collected more than 30 middens from 13 different Eciton army ant colonies in the rainforests at the in Costa Rica. After carefully sifting through the refuse, the researchers found more than 8000 adult beetles, some 500 beetle larvae, and two dozen eggs. One midden alone carried 2705 individual beetles.

By analysing DNA barcodes 鈥� short stretches of DNA that can be used to identify species 鈥� and studying the physical features of the scavengers, the researchers identified 91 different beetle species living in the refuse piles. The team even described two species that were new to science.

The middens appear to be a great place to raise beetle offspring. The team frequently spotted beetles mating within them 鈥� and for 22 beetle species, they found both adults and larvae present. The larvae may have been hatching from eggs in the waste heaps or crawling in from nearby.

鈥淚t appears likely that the middens play a crucial role in completing the life cycle of these beetles,鈥� says von Beeren.

The vast majority of the midden beetles are so-called rove beetles, many of which have evolved very close, symbiotic relationships with ants. at the California Institute of Technology in Pasadena wonders if using ant middens might facilitate the rove beetles鈥� eventual assimilation into the colony itself.

鈥淎rmy ant middens may be a stepping stone to closer associations with these host ants,鈥� says Parker.

The new findings underscore 鈥渢he role of army ant colonies as promoters of biodiversity in tropical rainforests鈥�, von Beeren says. But this is only one facet of the ants鈥� influence.

In addition to various colony symbiotes, there are 鈥渢he species that participate in army ant swarm raids, including antbirds, butterflies that feed on the birds鈥� droppings, flies and parasitic wasps鈥�, says von Beeren.

Army ant hordes are a magnet for hundreds of satellite species, and still more specimens from the study are waiting to be classified.