female black widow spider. Image: Wikipedia. Black widow spiders are notorious for their painful bites and lethal venom. The venom is potent enough to let these spiders and their close relatives prey upon small reptiles and mammals that other arachnids wouldn't ever eat. This raises the question: just what makes the widow spiders so unusually toxic? And how did they become so toxic to begin with? 
 
 Dr. Jessica Garb of the University of Massachusetts, Lowell, along with a team of collaborators in the US and the UK, has been attacking these questions by studying the spider's genetics, protein expression, and venom content, searching for clues about just how the widow spider's venom evolved to be so potent. 
 
 The most potent neurotoxins present in black widow venom are called latrotoxins, which takes its name from the group of widow spiders known as Latrodectus. The most toxic of these latrotoxins is alpha-latrotoxin, a devastatingly debilitating chemical that hijacks the body's own internal communications, the electrical and chemical signaling of the nervous system. 
 
 "If you got bitten by a black widow," says Garb, "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. This causes all of the neuron's vesicles to dump out their neurotransmitters. And that's really what's painful." In other words, alpha-latrotoxin causes nerve cells to release all of their chemical signals at once, overwhelming the nervous system, and causing immense pain. 
 
 In fact, alpha-latrotoxin has been studied for a long time by neuroscientists, not spider biologists, as a tool to help them understand how neurons function. And yet, until recently, the latrotoxins were thought to be a very small group of proteins. Garb's research has shown that latrotoxins are actually a much larger group than expected, and can even be found in the common house spider. But don't worry—the common house spider, though closely related to the black widow, is not generally considered toxic to humans. 
 
 The difference in venom potency between the widow spiders and the house spider may largely be a matter of the production of toxins, but not the genetic ability to do so. "It's not just about the numbers of these latrotoxins, but their relative expression," Garb says. Even though the genes for multiple latrotoxins exist in house spiders, they appear to be produced at much lower levels in their venom compared to black widows. 
 
 Genetics, of course, still has a role to play in the evolution of spider venom. "The house spider genome is a great resource for us, because we can now get the full landscape of what's in the genome of one of these spiders," explains Garb. By studying more than one species, the researchers could compare latrotoxin genes among closely-related species that vary in venom functionality and toxicity. 
 
 The researchers found that the latrotoxin genes among spiders, while clearly related, are highly divergent. "There has been a lot of lineage-specific evolution of this latrotoxin family, and the set of latrotoxins in house spider venom appears to be quite distinct from those in black widow venoms" says Garb. In other words, instead of having latrotoxin genes that have evolved slowly, gradually accumulating differences, the team believes that these genes have been duplicating and changing over a relatively short time period, contributing to the potency of black widow venom. 
 
 The fast appearance of multiple latrotoxins probably allowed the spiders to pursue a variety of prey items, including the small mammals and reptiles that widow spiders might not otherwise be able to eat. It's even possible that the widow spider's web changed along with the venom, becoming stronger to keep a hold on these larger prey. 
 
 In addition to discovering the diversity of latrotoxins within many species of widow spiders, examining the venom's composition revealed another trick up the widows' sleeves. After milking venom from the black widow spiders, Garb and her colleagues found that widow venom is actually made of many different types of toxins. And some of the contents of the venom were not just neurotoxins, but rather chemicals that likely help the toxins reach their targets within the body. So while we may have a good understanding of alpha-latrotoxin, scientists are only just beginning to appreciate the complexity and evolution of spider venom. 
 
 Garb presented her team's research findings at the 2015 annual conference of the Society of Integrative and Comparative Biology in West Palm Beach, Florida. 
 
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 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 ||||| Starting in 1996, Alexa Internet has been donating their crawl data to the Internet Archive. Flowing in every day, these data are added to the Wayback Machine after an embargo period.
– 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.)