[masraum]

Invasive Brown Widow spiders are killing off native black widow spiders.

https://www.smithsonianmag.com/smart-news/black-widow-spiders-are-being-killed-off-by-non-native-brown-widows-180981894/

With iconic red hourglass markings, shiny black bodies and a reputation as the deadliest spiders in North America, black widows have captured the public’s attention and imagination. But despite their infamy for being dangerous predators, new research reveals the arachnids have become prime prey for their less lethal cousins: brown widow spiders.

“Brown widows will aggressively go after black widows, chase them down,” Louis Coticchio, a biologist at the University of South Florida who led the study, tells the New York Times’ Asher Elbein. “They don’t play well with being neighbors.”

Their cousins, brown widows, originated in either Africa or South America but have managed to colonize every continent but Antarctica. They were first detected in the United States in 1935 in Florida and have since expanded across the South and parts of the West. But as the numbers of these non-native creatures increased, black widows seemed to disappear, writes Live Science’s Harry Baker. At first, entomologists thought brown widows were outcompeting the native spiders for resources, but with ample food and habitat in Florida, and with only black widows displaced, Coticchio wondered if something else was afoot.

To gain more insight into the interactions between the widow spiders, Coticchio and his colleagues placed a brown widow into a tank with either a southern black widow, a red house spider or a triangulate cobweb spider and recorded the outcome.

The results were dramatic: Brown widows were 6.6 times more likely to attack black widows than the other spiders. Young brown widows were particularly aggressive toward their cousins, killing and eating young black widows 80 percent of the time. In pairings of adults, black widows were eaten in 40 percent of the trials, while they defensively killed brown widows 30 percent of the time. The research team published the results this month in Annals of the Entomological Society of America.

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