The black widow spider is disappearing from the southern United States because the brown widow is hunting it

A group of researchers reported that the black widow spider is experienced a population decline in some areas of the southern United States due to an arachnid relative: the brown widow, as detailed in a study published Monday by the Annals of the Entomological Society of America.

The southern black widow (Latrodectus mactans), rknown for its dark color and red abdomenhas disappeared in recent decades from the southern state of Florida, while the brown widow (latrodectus geometricus), an African species detected in the USA in 1990, has been observed more regularly.

Both spiders are venomous, but the black widow has a reputation for being more dangerous to humans. The brown widow, who it is usually much more aggressive than the black widowhas a poison that generates milder symptoms, such as mild irritation.

Scientists thought that the decline in the population of black widows was due to an eventual fight for territory and food. However, experts realized that the brown widow preys on the black widow.

To verify this theory, specialists from the University of California at Riverside conducted an experiment in a laboratory. The brown widows were set against other species of spiderslike domestic reds (rufipes nesticodes), triangulated (Steatoda triangulosa) or black widows.

The study authors found that brown widows had 6.6 times more odds of killing black widows, regardless of their gender, size or stage of development, a rare phenomenon, since both arachnid species are closely related.

Even, and unlike the other species with which it interacted, the brown widow acted in a very aggressive way with the black widow, it was more daring and quickly attacked the hatchlings.

“We have established that brown widow behavior is very aggressive towards southern black widows, but much more tolerant of other spiders in the same familysaid lead author Louis Coticchio.

Brown widows “would kill them (black widows) before they even had a chance to react. They are very opportunistic”said research co-author Richard Vetter.

However, the black widow was also able to defend herself: “Sometimes a black widow on defense was able to catch the aggressive brown widowinto a spider web and inject venom into it,” the scientists observed.

Another factor identified by the researchers is that female black widows were smaller than those of the brown widow, and that They only laid one egg compared to the brown ones that put several simultaneously.