Why Do Spiders Bite You in Your Sleep?

by Derrick | Last Updated: July 18, 2022

If you’ve experienced an overnight spider bite, you may be wondering how the little critter got into your bed in the first place. More importantly, what did you do to deserve the bite?

Spiders bite you in your sleep when they feel threatened by your presence. If a spider got into your bed from a wall or another room, they believe they are safe hiding in the bed. When you crawl into bed at night you may unknowingly strike or corner them and they’ll bite to defend themselves.

Read on to learn more about why spiders decide to bite something as big as a human, how they do it, and when spider bites can be a medical concern.

Spiders Bite When Threatened

Even if a spider has wandered onto your bed, it’s unlikely to bite you without provocation. 

As the saying goes, “They’re more afraid of us than we are of them.” And if they feel threatened in any way, they are likely to bite.

Any type of direct contact with your body will give the spider enough reason to bite. For example, if you kick the spider in your sleep, graze it while rolling around, or touch it while repositioning your hand, it might go for the bite.

Fortunately, it’s rare for spiders to end up on your bed; your mattress needs to touch the wall or lay on the floor. Another way would be if you’re sleeping on furniture that is often unused, like a couch in a seasonal cabin.

If you see a spider in your bed before climbing in, try capturing it with a cup and paper and escort it out. Most of the time it’s a harmless spider you can safely get rid of without hurting.

Rather than on the bed, spider bites are more prone to happen in other household situations, like when you put on clothing that has been on the floor. Spiders often hide in household messes, so if you pick up a shirt or glove from the floor they may be hiding inside for the day. When you try to put it on, you scare the spider who will reflexively bite.

How Spiders Bite

Spiders have fangs on appendages called chelicerae. They use their fangs to immobilize prey with paralyzing, and sometimes disintegrating venom. In most species, this toxin does little more to humans than providing a brief sting.

Even when it comes to species that can harm humans, like black widows, most often the first bite is a warning. It lacks the potent venom black widows are known for. However, some deadly spiders, like the funnel web, may not be so courteous.

The Seriousness of Spider Bites

Even spiders with deadly bites are tiny arachnids, and the law of “they’re more afraid of you than you are of them” still applies. To get bitten by a spider you will have to threaten them first, knowingly or unknowingly.

While most spider bites are harmless, a few spiders have neurotoxins that can be dangerous to humans.

Black Widow Spiders

Black widows are among the most feared breed of spiders on the planet. They’re highly venomous, small, shiny, black, and have red warning marks on their backs.

They’ll fiercely protect their nests, which are usually hidden in enclaves and sometimes in a few rough spots in a messy house. This breed is common throughout North America and Australia.

We have named them ‘Black Widow’ because they eat their male partners after mating. However, most spiders perform this act after mating, so perhaps there’s another origin story to their names.

Black widow bites contain a neurotoxin that can cause nausea and muscle cramps. The main risk from black widows is to children and the elderly or feeble, as a single bite can lead to intense fever that may require hospitalization.

Funnel-Web Spiders

As the name suggests, these spiders create funnel-shaped webs, and they are found primarily in Australia. This breed is large and heavily built, much like the giant tarantulas you find there. Most funnel-webs aren’t dangerous to humans, but a few are, and they can even cause death.

As with black widows, the risk of death increases when the victim is a small child, the elderly, or the sick.

Brown Recluse Spiders

These tiny, reddish-brown spiders have a reputation in the American Midsouth. They inhabit a significant portion of Arkansas and a few neighboring states. This breed possesses a fiddle-shaped dark patch on their backs, which is unique to their species. 

Like many spiders, the Brown Recluse is harmless when left alone, and they will stay out as long as you keep your home clean. But despite your best efforts, you may cross paths with them once in a while.

Their bites can turn red and get very painful for hours. Luckily, most victims of this spider’s bite will recover on their own without medical care. 

However, sometimes people tend to experience fever, headaches, and nausea that may require medical aid.

Another alarming aspect of this spider’s bites is its necrotic properties. The term necrotic means “flesh-eating” and it’s called so because sometimes a bite creates blisters which lead to scarring as the blister eventually becomes dead tissue. As scary as this sounds, this symptom doesn’t typically require medical attention and will go away on its own.

Other Black Widow Relatives

Brown widows, red widows, white widows, and redback spiders are members of the black widow family and live in other parts of the world.

Brown widows look like black widows, but they’re brown and their red hourglass markings are orange. They inhabit places all over the world and are twice as venomous as black widows. Like most other spiders, they aren’t typically aggressive and won’t bite unless threatened.

Red widows are red all over with a different shade of red for the hourglass marking. Red widows are found in abundance mainly in Florida.

White widows live in several central Asian countries. This breed is differentiated by its light coloring, but otherwise looks just like the other widows.

Redback spiders were originally from Australia and eventually immigrated to New Zealand. The hourglass pattern can be found on its abdomen instead of where it usually lies on typical widows. Redbacks play dead in most interactions with humans but will bite if their eggs are threatened.

Other Causes of Night Bites

Quite often, the bumps on our bodies we wake up to and feel may not be from spider bites. Sometimes certain beddings may lead to bacterial growth, accumulation of oil and dirt, and collection of certain chemicals. All of these factors are more likely to irritate the skin than a spider bite.

Certain insects also may infest your sheets and mattress and bite you in your sleep. Some of these critters include fleas, bedbugs, mites, lice, and even ticks.

Final Thoughts

Spiders know that they are in a precarious position, being so small and fragile. As such, they tend to avoid humans as much as possible. However, in some cases, people will unwittingly corner a spider, compelling it to bite.

Certain situations, like putting on clothing that’s been lying around or using sheets that haven’t been properly dusted out can lead to interactions with spiders. Additionally, if your bed is against a wall or you have a mattress on the floor, you’re more likely to experience spider bites in the night.