Spider Widows War

vblack egg. In arachnophobes, this name alone causes palpitations. Actually, even people aware that almost all spiders are harmless are concerned at the mention of the small American specimen, with its black abdomen marked with a kind of bright red hourglass, and with its terrifying venom. This last qualification deserves to be put into perspective. Sharp pain, muscle spasms, nausea, tachycardia and hypertension: the bite of a black widow spider can be very unpleasant. But fatal cases remain extremely rare: just one deaths, discussed, in recent years. A US study concluded that only 3.75% of approximately 1,000 annual black widow spider bites cause acute symptoms. “I was bitten oncerecalls Louis Coticchio, a former poisonous species trainer who resumed his studies in zoology at the University of South Florida, and I felt only sharp pain and local inflammation at the injection site. »

The researcher reminds us: the black widow spider only uses its venom as a last resort, when it is subjected to pressure on its exoskeleton as a prisoner. “Otherwise she flees or she plays dead”, he said. In an article published March 13 in the Annals of the American Entomological SocietyCoticchio and two colleagues reveal that this character “shy” resulted in him being harassed and even regularly killed by the Brown Widow, a cousin who arrived from Africa nearly a century ago.

The researcher first noticed this in California, between 2014 and 2018: wherever the two species lived together, the black widow spider population declined. Back in his native Florida, he makes the same comment. “But I didn’t know the cause of this drophe says. Did black widows flee or were they murdered? We have started this research. »

The clash of two temperaments

Biologists first note a fertility that is twice as important in brunettes. However, this is insufficient to explain the imbalance. Thanks to mathematical models, they rule out the hypothesis of an escape due to a lack of food. In the end it is a container that has to reproduce their environment that the verdict falls.

Bruins and blacks are indeed not the only ones there. Two other types of spiders – Nesticodes rufipes et Steatoda triangulosa, the malmignatte of the houses – join the party. If the brown widow spider is generally the most aggressive, confrontations with these two species often end without harm. In contrast, the chance of a lethal interaction is 6.6 times greater in a black widow spider. Even worse, when a pre-adult brown female crosses paths with a young black widow, she attacks, kills and consumes her 80% of the time. Conversely, the researchers saw no aggression from black widow spiders.

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