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Hunters become hunted as brown widow spiders turn tables on deadly black cousins 

Studying the decline of black widow population, including the western ones, in US, scientists found that they were becoming prey of invasive brown widows (Pic. Courtesy wikimedia commons)

Looked at with fear, the world’s deadliest spider, the black widow, is now at the receiving end. These predators as per a new study have become chosen targets of their cousins, brown widow spiders in the United States as per a smithsonianmag.com article.

Talking about this, Louis Coticchio, who led the study observed: “Brown widows will aggressively go after black widows, chase them down. They don’t play well with being neighbours.” Coticchio is a biologist at the University of South Florida.

Shy by nature, the black widows live in dry and dark spaces close to human settlements. Though their bites are painful they are generally not lethal for human beings and in case of serious cases, antivenom provides relief.

It was christened as black widow as it is reputed to indulge in sexual cannibalism – devouring its mate after copulation. This is uncommon yet black widows continue to be notorious. The United States has three species of this creature – the northern, southern and western.

The brown widows don’t belong to the US and are native to South America or Africa. Yet they have spread all over the world except Antarctica. Their presence was first noted in Florida, US in 1935 after which they have rapidly moved to other parts. Their population increase synchronised with the numbers of black widows reducing.

Initially, this was ascribed to competition for limited resources but when this predation was observed in Florida where habitat and food are ample, it set scientists wondering. They placed the brown widows with southern black ones, a triangulate cobweb spider or red house spider.

What followed was astonishing. Black widows were 6.6 times more likely to be attacked by brown ones. This fierceness was prominent among the female brown widows who killed them 80 per cent of the time.

Details of the research have been published in Annals of the Entomological Society of America.

Commenting on the findings, Deby Cassill, the study’s co-author and an ecologist from University of South Florida said: “We didn’t expect to find such a dramatic and consistent difference in the personalities of the brown widow and the black widow. Brown widows are boldly aggressive and will immediately investigate a neighbour and attack if there is no resistance from the neighbour. The black widows are extremely shy, counterattacking only to defend themselves against an aggressive spider.”

Unable to explain this behaviour, the scientists now want to study if this is prevalent in other parts of the world. In Israel, too, the invasive brown widows are aggressive.

Browns have a natural advantage over their black cousins as they lay more eggs and start procreating earlier than them.

Brown widows are not considered invasive in the United States till now but when they become the reason for decrease in the population of black widows, will the attitude of scientists and people change? Time will tell.