What Makes a Spider Venomous?
If people suffer from arachnophobia (the fear of spiders and other arachnids) it is for a reason: the potent venom these creatures boast of.
Spiders are air-breathing chelicerates. They are typically characterized by an exoskeleton (an external skeleton), eight legs, and a modified front portion of their mouth used to inject venom. Statistics show that somewhere around 98 percent of the spider species on our planet are harmless, while the remaining 2 percent are potentially venomous, or "poisonous," as people usually call them.
There is a common confusion between the terms "venomous" and "poisonous" when it comes to spiders. The basic difference is that venom is injected into the body, whereas poison is taken orally. "Venomous" is the technically correct term for spiders and snakes (since these animals inject venom), but "poisonous" is the more common word in everyday use.
That 2 percent figure can be misleading. It only counts spiders capable of causing human fatalities with the amount of venom they deliver in a single bite. The truth is that only three of the roughly forty families of spiders, the Uloboridae family, Holarchaeidae family, and the Liphistiidae family, are non-venomous in nature. All other families are venomous to some degree. Depending on the species, spider bites can cause pain, itching, swelling, nausea, and even nervous system failure resulting in death.
Most Poisonous Spiders in the World
There are somewhere around 40,000 known species of spiders in the world, of which only around 200 are potentially dangerous to humans. That doesn't mean only these 200 have potentially lethal venom. Some species have more potent venom than others, but their fangs are not strong enough to penetrate human skin and deliver a lethal dose. While almost all spiders use venom for hunting, some use it mainly to defend themselves against predators.
Quite a few spiders have venom potent enough to kill an adult human. Species belonging to the Phoneutria, Atrax, Latrodectus, and Loxosceles genera already have human fatalities to their credit. Species belonging to the Hadronyche, Missulena, and Sicarius genera are also believed to carry venom potent enough to kill an adult.
Some spiders possess neurotoxic venom, which affects the entire nervous system of the victim. Others possess necrotic venom, which damages the tissues around the bite site.
Brazilian Wandering Spider
The Brazilian wandering spider was named the world's most venomous spider by the Guinness World Records in 2010. Also known as the banana spider or armed spider, it is a highly venomous spider belonging to the Ctenidae family of wandering spiders. Its native habitat ranges across Central and South America.
Like other wandering spiders, Brazilian wandering spiders (Phoneutria spp.) roam a lot on the forest floor, which increases their chance encounters with humans. This species accounts for a large share of human deaths from spider bites in the American continents.
Beyond its highly toxic venom, the Brazilian wandering spider is also extremely quick to attack anything that seems threatening, this combination makes it the deadliest spider species in the world. When threatened, it raises its body upright, lifts its two front legs high in the air, and sways its whole body from side to side to ward off the approaching threat.
Its venom contains the PhTx3 neurotoxin, which hampers muscle control, causes breathing difficulty, and can result in paralysis or asphyxiation. Of the various Brazilian wandering sub-species, Phoneutria fera (found in Ecuador, Peru, Brazil, Surinam, and Guyana) is considered the most venomous.
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Sydney Funnel-web Spider
Even though the Sydney funnel-web spider (Atrax robustus) delivers less venom than the Brazilian wandering spider, its fast-acting venom makes it a bigger threat. It is one of the various Australian funnel-web spiders belonging to the Hexathelidae family, and is found mainly in Sydney, Australia.
Resembling a tarantula in many ways, the Sydney funnel-web spider measures somewhere around 1 to 5 cm, is dark black or dark brown in color, and has a glossy outer covering. Its fangs are large and strong enough to pierce right through a fingernail, and combined with its potent venom, this makes it extremely dangerous. The Sydney funnel-web spider is also considered one of the most aggressive spiders because of its tendency to bite repeatedly and deliver a full dose of venom.
The different toxins in this spider's venom are collectively called Atracotoxins (ACTX). Interestingly, these toxins are harmless to wild animals but extremely dangerous to humans. The bite is very painful at first (because of its acidity and the size of the fangs) and it eventually leads to full-body envenomation.
A bite can cause nausea, vomiting, facial muscle twitching, profuse sweating, and excessive salivating. The victim may also experience shortness of breath, confusion, and high blood pressure. Further complications include low blood pressure and cerebral oedema (swelling of the brain), which can lead to coma or death. It is believed that the venom is so powerful it can cause death within just 15 minutes.
Black Widow Spider
The black widow spider (Latrodectus mactans) is a highly venomous species found in the United States and surrounding regions. The highest concentration of black widows is found in the southeastern United States, particularly Florida, Texas, and Oklahoma.
The black widow is one of many species of widow spiders (genus Latrodectus) found around the world. Female widow spiders practice the unusual ritual of sexual cannibalism, they kill and eat the male after mating. It is this behavior that gives widow spiders their striking name.
Females are shiny black in color and have a red or orange marking on the underside of their abdomen. Males in this species are noticeably smaller than females.
Though small compared to several other spiders, black widows possess extremely potent venom, which contains latrotoxins, polypeptides, adenosine, inosine, and 2,4,6-trihydroxypurine. This neurotoxic venom can cause severe pain, swelling, discomfort, and high blood pressure in humans.
Brown Recluse Spider
Also known as the fiddleback spider, brown fiddler, or violin spider, the brown recluse spider (Loxosceles reclusa) belongs to the Sicariidae family. It is found mainly in the United States and Gulf of Mexico.
The brown recluse is usually brown or deep yellow, with a black line running from the dorsal side of its cephalothorax. This black line looks like a violin with its neck pointing toward the rear of the spider, which is why it's called the violin spider. Unlike most spiders, which have four pairs of eyes, the brown recluse has just three pairs: one median pair and two lateral pairs.
These spiders generally shelter in cluttered spots, piles of wood or clothes, closets, garages, and cellars. They are not aggressive and only bite in self-defense. While a brown recluse bite is not painful at first, it can cause severe reactions throughout the body, which can sometimes be fatal.
Though bites are rare, they can be life-threatening because of the spider's potentially deadly hemotoxic venom. Most fatalities linked to the brown recluse involve small children or people with weakened immune systems.
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Redback Spider
The Redback spider (Latrodectus hasselti) belongs to the widow family of spiders and is considered the most dangerous spider found in Australia. It is also known as the Jockey spider or Kapara spider.
The female is black in color and has a red stripe on its abdomen. This species shows clear sexual dimorphism, female Redbacks are approximately 1 cm in length, while the males are much smaller.
Like the black widow, the female Redback kills and eats the male after mating. Female Redbacks are more aggressive than males, and they account for the vast majority of bite cases attributed to this species.
A Redback bite causes a clinical condition known as Latrodectism, triggered by the injection of neurotoxic venom. It produces extreme pain, swelling, headache, high blood pressure, heavy sweating, and a mild burning sensation. Though very rare, complications can include seizures, coma, and respiratory failure.
Venomous vs. Deadly: Not the Same Thing
While the Brazilian wandering spider holds the title of the world's most venomous spider, it is not the deadliest of the group. Several spider species are aggressive enough to strike with the slightest provocation. The Sydney funnel-web spider, for example, delivers less venom than the Brazilian wandering spider, but its large fangs, fast-acting venom, and aggressive nature make it more dangerous in practice.
Myths about spiders exist in abundance, and only when we look past them do we realize how fascinating these eight-legged creatures truly are, far more interesting than most people ever knew.
Fun fact for today!There are around 40,000 known spider species in the world, but only about 200 can seriously harm humans!