A Guide to the Most Common Spiders in Illinois
From city apartments to rural farmlands, spiders can be found in all corners of Illinois. While the majority of spiders pose no threat, some species can inflict painful and potentially dangerous bites. By learning to identify the most common spiders in your region, you can take precautions to avoid unwanted encounters.
Spider Anatomy and Behavior
All spiders share a similar anatomical structure with two main body segments, eight legs, fangs, and the ability to produce silk webbing. There are over 45,000 known spider species worldwide exhibiting a wide range of behaviors and habits.
Most spiders are not aggressive towards humans and will only bite as a means of self-defense. However, some species can be more confrontational when guarding egg sacs or webs. Understanding the threat levels and identification clues for spiders you may encounter can help avoid bites.
Venomous vs. Non-Venomous Spiders
While all spiders produce venom to subdue prey, most species cannot seriously harm humans. In Illinois, only the black widow and brown recluse spiders pose a significant health risk.
Spider bites can still cause mild reactions even if the species is considered non-venomous. Seek medical attention if you experience severe pain, swelling, nausea, fever or other concerning symptoms after any spider bite.
Most Common Spiders in Illinois
Here are some of the spiders you are most likely to find around homes, gardens, woodlands, and outdoor spaces in Illinois along with tips for identification:
1. Wolf Spider
- Size: Up to 1.5 inches
- Color: Brown, grey, black with light pattern
- Identifying Traits: Sturdy, hairy body. Large eyes arranged in rows. Swift runners.
2. Grass Spider
- Size: 0.5 inches
- Color: Yellow, tan brown, some stripe patterns
- Identifying Traits: Combfoot legs. Make horizontal sheet webs in grass and foliage.
3. Parson Spider
- Size: Over 1 inch
- Color: Brownish-grey with white and black markings
- Identifying Traits: Dark violin-shaped design on cephalothorax. Build messy webs under bark.
4. Barn Funnel Weaver
- Size: Up to 2 inches
- Color: Dark brown
- Identifying Traits: Robust body, long spiny legs. Make funnel webs in barns, sheds, and under logs.
5. Orb Weaver Spider
- Size: 0.4 - 1 inch
- Color: Variable combinations of yellow, black, white, brown
- Identifying Traits: Round, colorful abdomens. Build intricate circular webs outdoors.
6. Cellar Spider
- Size: 0.12 - 0.6 inches
- Color: Greyish-brown
- Identifying Traits: Extremely long, thin legs and small body. Irregular webs in dark corners.
7. Jumping Spider
- Size: Up to 0.5 inches
- Color: Variable colors like grey, black, brown
- Identifying Traits: Compact, fuzzy bodies. Jump to catch prey instead of building webs.
8. Sac Spider
- Size: 0.1 - 0.4 inches
- Color: Cheetah-like yellow and black or grey pattern
- Identifying Traits: Club-shaped abdomen. Nocturnal hunter without webs.
9. Crab Spider
- Size: 0.1 - 0.6 inches
- Color: White, yellow, green, brown
- Identifying Traits: Flattened oval shape. Ambush predators that don't use webs to catch prey.
10. Brown Recluse Spider
- Size: 0.25 - 1 inch
- Color: Uniform light to dark brown
- Identifying Traits: Violin-shaped marking on cephalothorax. Six equal-sized eyes.
Venomous Spiders in Illinois
Two types of venomous spiders are found in Illinois - the brown recluse and black widow. Their bites can cause severe reactions, so it is important to learn how to identify them.
Brown Recluse Spider
The most distinguishing feature of brown recluse spiders is the dark violin-shaped marking on their cephalothorax. These spiders build irregular webs in warm, dry, sheltered areas like attics, garages, and crawl spaces.
Brown recluse venom contains hemolytic compounds that break down red blood cells and cell membranes. This can create a necrotic sore at the bite site. Symptoms may include:
- Severe pain within 2-8 hours of bite
- Necrotic wound lesion
- Fever, chills, nausea
- Muscle pain and joint pain
- Rash, itching
- Headache, fatigue
Seek emergency care if bitten by a brown recluse spider, especially if wound sites appear.
Black Widow Spider
Female black widow spiders have a distinctive red hourglass marking on their jet black abdomens. They spin messy, tangled webs in dark sheltered spots like wood piles, tree hollows, and crawl spaces.
Neurotoxic venom affects the nervous system, causing symptoms such as:
- Localized pain spreading to abdomen
- Rigid abdominal muscles
- Nausea, vomiting
- Sweating, headache
- Hypertension, tachycardia
- Muscle spasms, tremors
Black widow bites require prompt medical treatment. Keep the bite site below heart level and seek emergency care.
How to Prevent Spider Bites
You can reduce your chances of being bitten using these spider bite prevention tips:
- Keep your home clean and clutter-free
- Wear gloves and protective clothing in crawl spaces
- Inspect or shake out items left in yards or garages
- Clear webs with brooms or sticks instead of your hands
- Install lights around entryways
- Apply pesticides sparingly and only if necessary
- Seal cracks and crevices around your homes exterior
If you encounter a spider, leave it alone and let it retreat. Never attempt to handle a spider unless properly trained. Bites often occur when trying to kill or capture spiders, so it's safest not to interact with them.
What to Do After a Spider Bite
If you are bitten by a spider, take these immediate steps:
- Wash the bite area with soap and water to reduce risk of infection
- Apply a cool compress to relieve swelling and pain
- Elevate the wound site if possible
- Take OTC pain medication if needed
- Monitor for signs of reaction or worsening symptoms
- Seek medical care if you experience severe symptoms or are bitten by a venomous spider
Bring the spider if captured safely for identification purposes. Prompt medical treatment is essential for dangerous spider bites.
Stay Vigilant of Venomous Spiders in Illinois
While the vast majority of spiders in Illinois are harmless to humans, key hazards include the brown recluse and black widow. Learning how to identify these venomous spiders and exercising caution outdoors and in undisturbed structures can help prevent bites.
If you are bitten by a spider, wash the wound, elevate, apply ice, monitor for symptoms, and seek emergency care for serious reactions. With proper education and precaution, spider encounters do not need to cause undue fear or harm.
FAQs
What are the most common spiders found in Illinois?
Some of the most common spiders in Illinois include wolf spiders, grass spiders, parson spiders, orb weavers, cellar spiders, jumping spiders, crab spiders, and sac spiders.
Which spiders are venomous in Illinois?
The two venomous spider species found in Illinois are the brown recluse spider and the black widow spider. Their bites can cause severe reactions.
How can I identify a brown recluse spider?
Brown recluse spiders have a violin-shaped marking on their cephalothorax and six equal-sized eyes. They make irregular webs in warm, dry, secluded areas.
What steps should I take if bitten by a spider?
Wash the bite, apply ice, elevate it, take pain medication, monitor for symptoms, and seek emergency care if you experience severe reactions or were bitten by a venomous spider.
How can I prevent spider bites at home?
Keeping your home clean, sealing cracks, inspecting items from storage, clearing webs carefully, installing lights around doors, and wearing protective clothing when in crawl spaces can help prevent bites.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.
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