Bio lure smells end for redbacks

The venomous Australian redback spider. Photo / Supplied

Chemicals based on pheromone produced by female showing promise as bait to entice males into traps

A cunning new weapon could spell the end for one of our most feared and unwanted pests.

The venomous Australian redback spider, characterised by the red strip across its swollen black abdomen, is found in several areas in Central Otago and New Plymouth, and its spread to other regions has remained a constant biosecurity worry.

Its incestuous nature means it can breed more freely than other species, and its thick web has helped it get past Customs checks.

But it's more notorious for the toxic venom that a single bite can deliver to a person unlucky enough to encounter one.

"One in three bites comes with a severe reaction, but even mild reactions aren't that mild," Otago University researcher Stacey Bryan said.

"They've been described to me as feeling like you're going to die for a period."

They also pose a worrying and growing threat to endemic species they prey on.

Ms Bryan has observed them predating 10 native species, including the nationally endangered Cromwell chafer beetle and the McCann's skink - the first time redbacks have been recorded attacking skinks since the spiders were discovered here in 1981.

She was concerned what this could mean for the endangered Otago and grand skinks, found throughout Otago, if redbacks became rampant.

Working with Canterbury Museum arachnologist Dr Cor Vink and other colleagues, Ms Bryan has developed a new biological control that could potentially stop their spread - and perhaps even wipe them out in New Zealand altogether.

It lies in two chemicals identified by Dr Vink, which were suspected to be the active ingredients in the pheromone that female redbacks laced their webs with to attract males.

"So my job was essentially to first see if males were attracted to these chemicals, and to see if we could make a biological control out of them," she said.

Her experiments found that while the chemicals weren't powerful enough to eclipse the attraction of the females' natural pheromones, they could still equal it - meaning at least half the males could be lured to their deaths in traps.

"So it still needs a bit of tweaking for us to get a super-stimulus, but we are three quarters of the way there."