brown widow spider
Shutterstock/Vinicius R. Souza
In parts of the southern United States, the black widow has given way to a more aggressive spider companion, the brown widow. However, residents of the area can take some comfort in knowing that brown widows are less toxic to humans than black widows. Symptoms after being bitten are usually limited to mild irritation similar to common house spider bites.
In recent decades, the number of Southern Black Widows (kill the robber) – Notorious for being identifiable by the red hourglass shape on its abdomen – Disappeared from Florida, brown widow (Latrodectos geotricus) has increased. Initially, scientists suspected that the decline in Black Widow numbers was related to competition for food and space from the Brown Widow, a species native to Africa that arrived in the United States in the 1990s. rice field.
The area appeared to have plenty of space and food for both spiders, so entomologists wondered if something else was going on. For example, black widows may have been sought out and hunted by brown widows.
To test the idea in the lab, Richard Vetter and his colleagues at the University of California gave brown widows a selection of arachnid buffets: red house spiders. (nest code ruphipes)to triangulate the web spider (Steatoda triangulosa) Or black widow. They found that brown widows were 6.6 times more likely to kill southern black widows in their enclosures than any other spider provided. It is rare for spiders to prey on organisms of the same genus (group of closely related species).
When researchers observed brown widows and southern black widows meeting face-to-face, they saw both species engaging in rapid bouts of “thumping” on each other’s legs. They also noted that brown widow females actively pursued, captured, and consumed southern black widows at all stages of development.
Brown widows behaved more aggressively than black widows toward other spider species offered, and showed no mercy to young spiders.[Brown widows] We were wiping them out before they could act,” says Vetter. “They are very opportunistic.”
Black Widow was not an attacker against Brown Widow, but she defended herself against them. “There have been times when a defending black widow was able to trap an aggressive brown widow in a sheet of webbing and inject her with venom,” the researchers wrote. Brown widows were also more daring and frequented black widows’ dens.
When researchers compared the two species, they found that female brown widows were superior to southern black widows in both size and fertility. A young female Brown Widow was 9.5% larger than the Southern Black Widow, and a mature female could lay multiple egg sacs at a time, whereas the Southern Black Widow she laid only one.
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