Poisonous Spiders: What You Need to Know

When it comes to poison, spiders are right up there on the list of creatures most people worry about. Almost everybody has heard of the black widow spider, or at the very least, seen a comic book hero who got his powers from a radioactive spider bite. But is the fear of a poisonous spider warranted? This checklist will help put all your questions to rest.

Are all spiders poisonous?

All spiders possess venom that is toxic, or poisonous, to an extent. Spiders use their venom for a number of reasons, including incapacitating prey, for self-defense and in some species of spiders, on their mate before devouring them. But not all of the poison spiders produce is harmful to humans.

In fact, of the more than 3,000 types of spiders in the United States, only around 60 species have venom that is deemed ‟medically significant” when introduced to a human’s blood stream. So, while all spiders are poisonous, most of them cannot harm you.

How often do spiders bite?

Further reducing the instance of poisonous spider bites is the fact that most spiders can’t even break through human skin with their tiny fangs. Of the spiders that can inflict a puncture wound, many possess venom that doesn’t cause a reaction in humans. As if that didn’t deflate the ‟deadly spider myth” enough, about 80 percent of all suspected spider bites actually come from insects and other arthropods.

Spiders are timid by nature. They have soft bodies and are very fragile, so their first instinct is to run and hide when confronted. They will only bite a human when cornered, injured, forced or mishandled. Even if a spider with medically significant poison does bite you, venom isn’t always injected. The spider uses discretion and injects venom proportionate to the perceived threat. So, it’s unlikely you will randomly be bitten by a spider and even if you are, it’s even less likely you will be poisoned to the point of nearing death.

How deadly are medically significant poisonous spider bites?

Of course, people do get bitten by potentially deadly spiders, but the risk of dying depends on the type of spider, the person’s reaction to the venom, the location of the bite on the body and their proximity to medical treatment. Thanks to the widespread availability of antivenoms and other spider bite treatments, there are rarely any deaths related to spider bites anymore. No species of spiders kill within a few minutes, as you might see in Hollywood, so there is ample time to get treatment for any poison spiders might inject into you.

According to the Oklahoma State University Cooperative Extension Service and Centers for Disease Control, there may be other complications such as infections, rashes, loss of skin tissue and possibly even organ failure involved, but death is a rarity. Spider bite reactions can become complicated if the person is allergic to the venom or saliva of the spider, meaning even a typically non-toxic spider bite can create problems. Other people susceptible to significant impact from a spider bite include those with compromised immune systems, preexisting medical conditions or children and the elderly.

What does a black widow spider look like?

Black widows are the most venomous spiders in the United States. Only the female of this species carries the potent neurotoxins that can harm humans. Fully extended females measure about 1.5 inches in length, while males are generally about one-half of an inch smaller. The widow’s hairless black body is glossy and shiny. Females have the notorious red hourglass marking on the underside of their round abdomens, while males have three light streaks on their abdomens and knobby appendages on their heads. Both sexes have eight eyes arranged in two rows.

Where are black widows found?

Since they are vulnerable when they stray too far, females stay close to their silk tunnel webs during the day, hanging ‟belly up,” exposing their natural red warning sign. These poisonous spiders are shy and prefer to stay in secluded areas such as sheds, attics, garages, crawl spaces and under window eaves. Their crisscrossed webs are generally found around boxes, crates, shrubbery, wooden planks, firewood piles, trash cans, under stones and inside water or gas meter casings. They can be driven inside homes, buildings and other structures by cold and drought.

What does a black widow bite look and feel like?

Black widow bites are immediately noticeable and painful. Two red, tiny puncture wounds mark the spot of the bite. Pain typically intensifies for approximately three hours, first at the site of the bite, then throughout the body. The agony continues steady for 12 to 48 hours. Eventually, the pain gradually subsides.

This general suffering can be accompanied by other symptoms of a black widow bite, including back pain, chills, violent abdominal spasms, delirium, dizziness, headache, vomiting, profuse sweating, skyrocketing blood pressure, limb rigidity and shortness of breath. These symptoms can often be misdiagnosed as food poisoning, colic or appendicitis.

Left untreated, death by asphyxia can occur in young children and those in poor health. This typically happens within 12 to 32 hours after being bitten. Healthy adults seldom die from being bitten by this poisonous spider, recovering within one to five days. The overall mortality rate for black widow bites is believed to be around 1 percent or less. A commercial black widow antidote is available, so all bites should receive immediate medical attention, no matter how healthy you are.

What does a brown recluse look like?

Another potentially deadly poisonous spider common to the U.S. is the brown recluse. This spider’s tan to dark-brown body has a dark marking on top that looks like a violin or fiddle, lending to its two nicknames, the ‟fiddleback” or ‟violin spider.” The ‟neck” of the violin points to the rear, with this spider’s unique six eyes (instead of the typical eight) located towards the base of the ‟instrument.” These spiders range in size from one-quarter to three-quarters of an inch in length.

Where are brown recluses found?

Brown recluses tend to avoid any areas where humans are active. Inside the home, they can be found in closets, attics, basements and low-activity rooms, such as vacant guest rooms and bathrooms. They seek shelter during the day, inhabiting furniture, baseboards, old clothing, corners, crevices and storage boxes. Outside the home, they can be found in sheds, barns and garages, as well as underneath rocks. At night, they come out to hunt prey such as crickets, roaches, silverfish and other insects.

What does a brown recluse bite look and feel like?

Because of these hiding spaces, most people who are bitten by these poisonous spiders receive bites around the hands or feet when they handle infested items. Bites are typically painless at first, with a burning sensation developing around the site of the bite within one to three hours. Over the next six to 12 hours, a hard blister or pimple appears at the site of the wound and the victim might become restless and feverish.

The venom of the brown recluse causes a necrotic reaction, resulting in the skin tissue around the bite to darken, harden and swell. Extensive tissue damage can continue to occur for the next two weeks. During this time, the blister or pimple might turn into an open ulcerated sore as the cytotoxic venom eats away at the skin and exposes the underlying muscle. The resulting sore is sunken into the body and can measure up to a few inches in diameter. In some rare instances, kidney or liver damage might result from systemic complications.

Over the next six to eight weeks, the bite will heal, though larger, sunken scars might require surgery and skin grafts in order to repair tissue damage. Though specific antivenom for the brown recluse isn’t available, seeking immediate medical attention is important as it can prevent necrotic reaction and the ensuing ulcerated sores and scars from occurring.

What are the world’s most poisonous spiders?

There is much debate over which spider is the most ‟deadly” in the world. Realistically, there aren’t many deaths due to spider bites anymore, and there haven’t been for decades. Figuring out the ‟most deadly” would entail injecting humans with venom on purpose, which isn’t only impractical, but unethical. It’s widely accepted that the most potentially deadly poison spiders produce comes from Brazilian wandering spiders, Sydney funnel web spiders, redback spiders, white-tailed spiders, yellow sac spiders, black widow spiders and brown recluse spiders. Of this list, only the black widow and brown recluse are native to the United States.

If you suspect you’ve been bitten by any type of spider, seek immediate medical attention. If at all possible, try to capture the offending spider for identification purposes. Most bites can’t be identified without first identifying the spider (until it’s too late, as is the case with the brown recluse). Poisonous spider or not, it’s better to be safe than sorry.

The same goes with your house – if you’re experiencing spiders in your home, call Terminix® for a free pest estimate and get the peace of mind you deserve. They may not always be poisonous spiders, but they shouldn’t be in your home.