The painful bites and lethal venom of black widow spiders have evolved rapidly over the years, according to a new study that also found common house spiders produce similar toxic compounds.
The difference is that female black widows produce ample amounts of highly potent venom to the point that these spiders are even crafting stronger webs to handle ever-bigger prey. The findings were presented at the 2015 annual conference of the Society of Integrative and Comparative Biology in West Palm Beach, Fla.
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The most powerful neurotoxins present in black widow venom are called latrotoxins, which take their name from the group of widow spiders known as Latrodectus. The most toxic of these latrotoxins is alpha-latrotoxin that hijacks the poor victim's own nervous system.
"If you got bitten by a black widow, alpha-latrotoxin would travel to the pre-synaptic regions of your neurons: this is the juncture right between the synapse of one neuron and your muscle cells or another neuron, and it inserts itself into the membrane," explained Jessica Garb of the University of Massachusetts, Lowell, in a press release.
She added, "This causes all of the neuron's vesicles to dump out their neurotransmitters. And that's really what's painful."
Garb and her colleagues determined that latrotoxins are more common in the world of arachnids than previously thought. Many spiders produce the toxins to help with their own hunting, but they make such a watered down version that they're not harmful to most people.
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Female black widows, on the other hand, have quickly evolved super concentrated venom that can kill a person. Each year, about 2,200 people report being bitten by a black widow, but most recover within 24 hours with medical treatment.
Many people who are bitten develop few symptoms since the spider may not inject its venom. Black widows are actually not very aggressive spiders, so you really have to startle or otherwise threaten one to get a hostile reaction.
As for why black widows, in particular, have evolved such potent venom, Garb and her team think it was to expand the spider's diet. Black widows can consume small mammals and reptiles, in addition to more typical smaller prey. As their name suggests, females may also kill their mates, so it seems they are not averse to eating most things.
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The researchers also discovered that black widow spider venom contains a cocktail of other toxins that boosts the effectiveness of alpha-latrotoxin.
Understanding spider venom could lead to better treatments for bites. Some scientists also believe that the venom holds untapped medical benefits. Research is ongoing, for example, on how latrotoxins and related compounds might hold the keys to treating Alzheimer's, cancer, pain, and even sexual problems.
Photo: A female black widow spider. Credit: James Gathany, CDC