Spider Widows War

Spider Widows War

Black Widow (Latrodectus mactans) adult female, Florida.

Vblack egg. In arachnophobes, this name alone causes palpitations. As a matter of fact, even humans aware that almost all spiders are harmless worry at the mention of the small American specimen, with its black abdomen marked with a sort of bright red hourglass, and with its fearsome venom. This last qualifier 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: only one deaths, discussed, in recent years. A US survey concluded that only 3.75% of the approximately 1,000 annual bites from black widow spiders cause acute symptoms. “I was bitten oncerecalls Louis Coticchio, a former trainer of venomous species who resumed studying zoology at the University of South Florida, and I only felt sharp pain and local inflammation at the injection site. »

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

The researcher first noticed this in California, between 2014 and 2018: wherever the two species cohabited, the population of black widow spiders was decreasing. Back in his native Florida, he makes the same observation. “But I didn’t know the cause of this declinehe says. Did black widows flee, or were they killed? We started this research. »

The clash of two temperaments

Biologists first note a fertility twice as important in brunettes. Insufficient, however, to explain the imbalance. Thanks to mathematical models, they rule out the hypothesis of a flight resulting from a lack of food. It is ultimately a container supposed to reproduce their environment that the verdict falls.

Browns and blacks are indeed not alone there. Two other species of spiders – Nesticodes rufipes And Steatoda triangulosa, the malmignatte of the houses – take part in the celebration. If the brown widow spider is generally the most aggressive, its confrontations with these two species often end without damage. In contrast, the probability of a fatal interaction is 6.6 times greater with a black widow spider. Worse: when a pre-adult brown female crosses paths with a young black widow, she attacks, kills and consumes her in 80% of cases. Conversely, the researchers observed no aggression from black widow spiders.

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