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 reports. 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. "If you got bitten by a black widow," says study co-author Jessica Garb, "alpha-latrotoxin would travel to the pre-synaptic regions of your neurons ... and it inserts itself into the membrane."
"This causes all of the neuron’s vesicles to dump out their neurotransmitters," she adds. "And that’s really what’s painful." Put another way, alpha-latrotoxin makes nerve cells unleash all of their chemical signals together, swamping the nervous system and inflicting massive pain, phys.org reports. The study, presented at the Society of Integrative and Comparative Biology, also says black widows may have evolved to spin stronger webs that can hold larger victims like reptiles and small mammals. Researchers add that black-widow venom holds extra chemicals that help its neurotoxins hit targets in the human system—so scientists are "only just beginning to appreciate the complexity and evolution of spider venom," says phys.org. (See how surgery removed a man's fear of spiders.)