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Why are black widow spiders so deadly?

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Black widow spiders are known for their lethal venom, but just how did they get so deadly? Apparently by evolving quickly over the years during their pursuit of "ever-bigger prey," Discovery... Science News Summaries. | Newser. read more

The spiders jaws and poison says:"The poison of a black widow spider has a LD50 of 0.9 mg per kg mouse.That is 0.013 mg per mouse. The spider needs 2 mg to kill half of the frogs. So the lethality differs among animals. Horses, cows and sheep are more sensitive to black widow spiders than humans. read more

According to a new study, black widows and house spiders have comparable toxic compounds in their venom—but black widows evolved faster and became far more dangerous. The common compounds are called latrotoxins; the black widow, however, produces alpha-latrotoxin, which takes over an unlucky victim's nervous system. read more

"Black widow spiders belong to the family Theridiidae, commonly referred to as comb-footed spiders," Sewlal said, adding that comb-footed spiders get their name"because they have a series of stiff short hairs on the last segment of their fourth pair of legs that resemble the teeth of a comb. read more