Are All Spiders Venomous? Venom vs Real Danger to People

Why nearly all spiders have venom

Spiders are predators, and venom is their main hunting tool. A spider’s jaws, called chelicerae, end in hollow fangs connected to venom glands. When it bites, venom flows through the fang into the prey, paralyzing or killing it within moments.

Spider venoms are complex mixtures, often containing hundreds of different proteins and small peptides. Most of these target the nervous systems of insects and other invertebrates, the spider’s usual food. Because spiders cannot chew solid food, they then flood their prey with digestive juices and suck up the liquefied tissue. A crab spider holding a honeybee, or a garden spider wrapping a fly, has used venom to make that meal possible.

Which spiders have no venom?

Only a handful of spiders have lost their venom glands. The best known are the hackled orb weavers of the family Uloboridae. They capture prey in webs made of fluffy, dry silk and then bind it in many layers of silk before digesting it, with no venomous bite at all. One species, the feather-legged spider Uloborus plumipes, has become common in greenhouses in Europe.

Some primitive segmented spiders of East Asia, relatives of the earliest spider lineages, also lack venom glands. Every other spider people are likely to meet, from the tiny money spiders of lawns to giant tarantulas, has venom.

Some creatures that are often called spiders are not spiders at all. Harvestmen, also known as daddy longlegs, belong to a separate group of arachnids and have no venom glands. The famous claim that daddy longlegs are deadly but cannot bite is a myth, explained in are daddy longlegs venomous?

Venomous vs poisonous: what is the difference?

The two words are often mixed up, but they describe different things:

• Venomous animals inject a toxin, usually through a bite or sting. Spiders, scorpions, bees and rattlesnakes are venomous.
• Poisonous animals are harmful when they are eaten or touched, because their tissues or skin contain toxins. Poison dart frogs, pufferfish and monarch butterflies are poisonous.

So spiders are venomous, not poisonous. A “poisonous spider” is a common but inaccurate phrase.

Why most spiders cannot hurt you

Several things stand between a spider’s venom and a person:

• Fang size and strength. Many spiders are only a few millimeters long, with fangs too short or weak to pierce human skin.
• Venom tuned for insects. Most spider toxins evolved to act on insects and have little effect on mammals.
• Tiny doses. Even a spider with potent venom injects only a minute amount, and many defensive bites are “dry”, with little or no venom.
• Behavior. Spiders do not hunt people. They bite only in self-defense, usually when pressed against skin in clothing, shoes or bedding.

When a common spider does bite, the result is usually a brief, sharp pain with some redness and swelling, often compared to a bee sting. Typical examples are covered in are house spiders dangerous?

Many “spider bites” are not spider bites at all. A 2016 review of 134 published medical case reports found that 78% did not meet the criteria for a verified bite, and skin infections are often blamed on spiders that were never seen.

The spiders that are dangerous to people

Medically significant spiders make up well under 1% of all species, and most belong to four groups:

The Sydney funnel-web spider caused 13 recorded deaths before an antivenom became available in 1981, and none since. Widow spiders, such as the southern black widow, and recluses, such as the brown recluse, are the only US spiders of real medical importance. A few others, including the six-eyed sand spiders of southern Africa, have strong venom in laboratory tests but few or no well-documented human bites. The full ranking is in most venomous spiders.

Spiders in Europe: venomous but rarely risky

Europe has no spiders as dangerous as funnel-webs. Around the Mediterranean, the Mediterranean black widow can cause painful bites, and the Mediterranean recluse lives in parts of southern Europe. In central Europe, the yellow sac spider Cheiracanthium punctorium has a bite that is painful but not dangerous to healthy people.

Britain and Ireland have no native spiders that are dangerous to healthy people. The noble false widow, now common in and around buildings, can bite, but its bite usually feels like a wasp or bee sting.

Should you worry about spider venom?

For nearly everyone, no. Spiders are some of the most useful predators in gardens and homes, eating huge numbers of insects. Researchers are even studying spider venom peptides as possible painkillers, treatments to protect the brain after a stroke, and insecticides that target pests without harming mammals.

The sensible approach is respect, not fear: do not handle spiders you cannot identify, wear gloves when moving wood or stored items, and shake out shoes left outdoors. If someone is bitten by a spider that might be dangerous and develops severe pain, cramps, sweating or difficulty breathing, seek emergency medical help immediately: call 911 in the US, 112 in the EU or 999 in the UK.