Venomous (Poisonous) Spiders in Illinois

Illinois is home to over 500 species of spiders living in different habitats across the state. While they worry many homeowners because they’re often seen as bizarre and scary, the majority of spiders found in Illinois are actually harmless. Two particular species – the black widow spider and the brown recluse spider – are an exemption. You don’t want to be anywhere close to these deadly spiders! A bite from them can be dangerous, as they inject highly toxic venom capable of causing life-threatening symptoms in humans. For this reason, spider bites such as this are correctly referred to as ‘venomous’, not ‘poisonous’. 

Unfortunately, black widow and brown recluse spiders are widely distributed throughout Illinois, so it’s important to know how to identify them so you can try your best to avoid facing their wrath. This article talks about what these venomous spiders in Illinois look like, where you’re likely to find them, what the symptoms of a bite are, and what you should do if you’re unfortunately bitten by any of these deadly arachnids.

Venomous Spiders in Illinois

1. Black Widow Spider

The most common venomous spider in Illinois is the black widow spider. Here’s what you should know about them.

How to Identify a Black Widow Spider

Almost everyone in Illinois should be able to recognize a black widow spider when they see one. They are easily identified by their striking black and shiny appearance with red hourglass markings on the underside of the females. Sometimes, there’s a row of red spots visible on top of them too. Female black widows are about an inch and a half to 2 inches long while the mature male of this species appears smaller —about half the size of the female. But note that the males have longer legs and may have several white and red markings on the dorsal side and an orange or red hourglass marking on the underside. 

Where Do Black Widows Live in Illinois?

Black widow spiders usually prefer to live in dimly lit locations and dark corners. This is why you’ll likely find them in the basement, closets, and cluttered areas in and around the home. Because they don’t like moisture and prefer dry areas, the best places to look for them in Illinois include tree stumps, overhanging ledges, under rocks or benches, near entrances to abandoned rodent burrows, around outbuildings, and in various kinds of structures. This dangerous spider is nocturnal and mostly active at night. 

Black Widow Bite Symptoms

A black widow spider is not naturally aggressive. They only bite when provoked or disturbed. Females, especially, have been known to bite if their web is disturbed, usually in defense of their eggs. However, it is important to know that the venom of the black widow is highly toxic—said to be 15 times stronger than that of a rattlesnake! The venom is neurotoxic and majorly affects the nervous system. The first symptoms you’ll notice when bitten by a black widow spider are immediate and intense pain, as well as swelling and redness around the bite area. Some people are only slightly affected by the bite while many others have severe reactions to it. Abdominal pain and cramping, headache, sweating, dizziness, sweating, and pain in the chest are a few of the common symptoms of a black widow bite. In severe cases, paralysis of the legs, weakness, and tremors are seen. 

2. Brown Recluse Spider 

Brown recluse spiders are, by far, the most widespread brown spiders in the United States. Also one of the two venomous spiders found in Illinois, here’s what you should know about them. 

How to Identify a Brown Recluse Spider

Brown recluse spiders are brown, orange, or tan in appearance. Their head is often darker with a total of six eyes arranged in a triad of three pairs, which is their main distinguishing feature. Oftentimes, the brown recluse has faint or distinct violin-shaped markings on its back, which can help to easily identify it. But this is not very reliable, as there are other spider species with similar markings. The length of adult male and female brown recluse spiders ranges from 0.24 to 0.79 inches. These spiders have very long light brown legs, usually a lot longer in proportion to their body.

Where Do Brown Recluse Spiders Live in Illinois?

Brown recluse spiders are both indoor and outdoor species in Illinois. Found in the whole of northern and southern Illinois, they are nocturnal spiders who prefer to live in dry, dimly-lit, and secluded places. You’ll likely find them in dark places such as low-traffic basements, cluttered areas, attics, and closets. Look out for them also on wooden surfaces such as inside cardboard boxes, furniture, wall voids, and wood framings. Some Illinois residents have reported seeing them inside their beds and shoes. Because they live indoors and look like many common types of house spiders, most people don’t even know that they’re looking at a dangerous venomous spider when they come across a brown recluse!

Brown Recluse Bite Symptoms

Despite their reputation as the deadliest spider species in North America, brown recluse bites are rare. This spider is not an aggressive species — they’re reclusive by nature and prefer to retreat from humans and hide. You can only get bitten if you accidentally step on them or trap them between your body and clothing/bedding. The brown recluse bite is usually painless at first but may later cause swelling, itchy redness, and burning pain a few hours after the bite. Other bite symptoms include headache, nausea, fever, vomiting, rash, or body aches. The bitten area and skin around it may look purplish or dark blue in appearance due to the necrotic venom of the brown recluse spider. Severe necrosis results in an excruciating “flesh-rotting” wound that may be slow to heal and sometimes leads to secondary infections. In mild cases, bites may heal on their own, but medical treatment is required if it gets worse. Death from brown recluse bites has been reported, but is extremely rare and possibly occurs only in children or vulnerable individuals.

What Should You Do if You are Bitten by a Venomous Spider in Illinois?

Bites from venomous snakes can result in serious medical complications. If you suspect that you’ve been bitten by a venomous spider, the first thing to do is to seek immediate medical attention. Call 911 immediately if you realize that you have trouble breathing, as this can indicate that you’re having an allergic reaction. If possible, it is helpful to try to capture the spider that has bitten you so that medical professionals at the hospital can identify the spider and determine the correct treatment for you. 

In addition, it’s important to remember that spiders avoid humans, and even the venomous ones would rather run away from you than bite. They only bite as a last resort when they feel threatened or cornered. So if you come across either the black widow or brown recluse spiders in Illinois, it is best to leave them alone and go your own way.

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