Long Forgotten Wasp Holds Key to Control of Annoying Redback Spiders

The wasp Agenioideus nigricornis that was lost more than 200 years ago is now being discovered as a predator of Australia's most common dangerous spider, the redback. And, the scientists are excited as the redback spider is most obnoxious pest of Australian homes and they seem to have found natural remedy to eradicate it.

The redback spider (Lactrodectus hasselti) is an Australian relative of North America's black widow spider.

An event of the wasp dragging the spider to its nest was noticed by Florian Irwin. This episode was photographed by his father, Dr Peter Irwin, who even kept the specimens.

Peter, an Associate Professor at Murdoch University, contacted the Western Australian Museum about the discovery; the Museum updated Professor Andy Austin from the University of Adelaide's Australian Centre for Evolutionary Biology & Biodiversity and research fellow Dr Lars Krogmann at the University of Adelaide.

"The Museum knew we were doing research into the Agenioideus, which belongs to the family Pompilidae, the spider-hunting wasps. Little is known about them, despite various species of Agenioideus being distributed throughout the world," Professor Austin says.

"We're very excited by this discovery, which has prompted us to study this species of wasp more closely. It's the first record of a wasp preying on redback spiders and it contributes greatly to our understanding of how these wasps behave in Australia."

It was in 1776 that the wasp was first described scientifically by Danish entomologist Johan Christian Fabricius.

"Since then, scientists have largely forgotten about the wasp," says Austin. "It is widespread across Australia and can be found in a number of collections, but until now we haven't known the importance of this particular species."

The wasp that is no longer than its prey stings and paralyses the redback spider and takes it to its nest where it lays an egg on it. The spider remains alive but is paralyzed. Once the egg hatches, the larval wasp feeds on the spider.  

"The redback spider is notorious in Australia, and it has spread to some other countries, notably Japan and New Zealand. Redbacks are one of the most dangerous species in Australia and they're mostly associated with human dwellings, which have been a problem for many years," Professor Austin says.

"The redback spider-hunting wasp is doing its part to keep the population of redback spiders down, but it doesn't hunt all the time and is unlikely to completely eradicate the spiders."