(ORDO NEWS) — Ecologists have found that the decline in the numbers of two species of American black widows is due to the penetration of African brown widows into the southern United States, whose females often attack and kill smaller American black widows.
“Our observations have shown that female brown widows are extremely aggressive towards black widows, but they do not attack other spiders from the same family.
Now we are interested in whether these spiders behave differently in African ecosystems, where they come from. presumably spread around the world,” said Luis Coticchio, a researcher at the University of South Florida (USA), quoted by the ESA press service.
Black widows are a genus of large predatory spiders, they are found on all continents of the Earth. In total, scientists have over 30 varieties of black widows, most of which live in the New World. Many species of these spiders produce powerful neurotoxins, some of which are dangerous to human life.
In recent years, Coticchio and his colleagues note, scientists have begun to notice that the numbers of the two most common species of black widows in the US south, Latrodectus mactans and Latrodectus hesperus, have begun to decrease.
At the same time, the territories abandoned by black widows began to be occupied by other large spiders, African brown widows (Latrodectus geometricus), accidentally introduced to the New World in the last century.
Black and brown widows
American ecologists have suggested that these changes in the numbers and habitats of two different species of spiders may be related.
So, they studied the conditions in which brown and black widows live in different regions in the southern United States, and followed the interaction of spiders with other invertebrate creatures.
Observations have shown that both types of widows do not experience problems with the extraction of food – they die much more often from attacks by other predators and large animals than from a lack of nutrients.
At the same time, scientists revealed discrepancies both in the growth rate and size of female spiders, and in the reaction of brown and black widows to aggression from “competitors”.
Specifically, the researchers found that young female African brown widows were about 10% larger than similar-aged black widows, yet they reached puberty 16% faster and produced, on average, twice as many offspring.
In addition, biologists have found that female brown widows purposefully attack and kill about 80% of their “competitors” among black widows, but they are much less likely to show aggression towards other types of spiders.
Such behavioral patterns in brown widows, Coticchio and colleagues believe, explain why the number and range of black widows in the southern United States have declined in recent years.
What is the reason for the behavior of brown widows, scientists cannot yet say, but they hope that observations of the life of Latrodectus geometricus in Africa will provide an answer to this question.
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