A Guide to Common and Venomous Spiders in Iowa

Introduction to Common Spiders in Iowa

Iowa is home to a diverse array of spiders, ranging from the harmless and helpful to the potentially dangerous. While the majority of spiders in the state pose no threat to humans, Iowa is within the natural habitat range of two spiders with medically significant venom - the brown recluse and black widow spiders. Knowing how to identify these spiders, as well as being familiar with common non-venomous species, can help Iowa residents coexist safely with these fascinating creatures.

Why Are Spiders Important?

Spiders play a vital role in ecosystems by helping to manage insect populations. As predators, they help keep pest insects like mosquitoes, flies, roaches, and agricultural pests under control. Their venom also contains compounds that may have potential medical applications. While a bite from a venomous spider can cause harm, spiders are not malicious creatures - they bite only in self-defense when threatened or unintentionally provoked.

Web-Building vs. Hunting Spiders in Iowa

There are two main groups of spiders in Iowa - web-building species like orb weavers, and hunting spiders like wolf spiders and jumping spiders. Web-builders snare prey in sticky silk while hunting spiders actively pursue their prey. Both play an important role in controlling insect populations, with web-builders catching flying insects and hunters capturing ground-dwelling bugs.

Common Web-Building Spiders in Iowa

Orb Weavers

Orb weaver spiders are some of the most familiar web-building spiders in Iowa. They spin large, circular webs with radial threads and sticky spirals to capture flying insects like moths, flies, bees, and grasshoppers. Common Iowa orb weavers include:

• Garden spiders - large, hairy black and yellow spiders in the genus Argiope. They are often found in gardens, fields, and forests.
• Barn spiders - spiders in the genus Neoscona that build their webs on barns, sheds, and other structures.
• Marbled orb weavers - medium-sized spiders with an abdomen patterned with gray, brown, and cream. They build webs in vegetation.

Orb weavers are harmless to humans, although they may bite if carelessly handled. Their venom is not considered medically significant.

Funnel Weavers

Funnel weaver spiders build sheets or funnel-shaped webs on the ground, in leaf litter, or against the walls of buildings. Common examples in Iowa include:

• Grass spiders - long-legged, dark brown spiders found in lawns, fields, and meadows.
• Barn funnel weavers - large brown spiders that build funnel webs in barns and sheds.
• Cellar spiders - also called "daddy longlegs," these spiders build irregular webs in corners of cellars and crawlspaces.

Funnel weavers are not aggressive and rarely bite humans. They help control insect pests by catching them in their ground-based webs.

Common Hunting Spiders in Iowa

Wolf Spiders

Wolf spiders are medium to large hairy spiders that actively hunt instead of building webs. They have excellent eyesight and chase down prey. Common Iowa species include:

• Rabid wolf spiders - large, brown spiders with longitudinal stripes found throughout the state.
• Carolina wolf spiders - brown or gray spiders with longitudinal stripes common in wooded areas.
• Tiger wolf spiders - black with white markings, found in gardens and fields.

Wolf spiders help control pest populations but will bite in self-defense if threatened. Their venom is not considered dangerous.

Jumping Spiders

Jumping spiders are compact, hairy spiders that actively hunt during the day. They have excellent vision and jump on their prey. Common Iowa species include:

• Daring jumping spiders - small and fuzzy black spiders with large forward-facing eyes.
• Bronze jumping spiders - iridescent brown, green, and orange spiders found on plants.
• Gray wall jumpers - small gray spiders that frequent walls of buildings and rocky cliffs.

Jumping spiders pose no threat to humans. Their bites are uncommon and not harmful.

Venomous Spiders in Iowa

While most Iowa spiders are harmless, two species can inflict painful and medically significant bites - the brown recluse and black widow spiders. Proper identification and control measures can help prevent bites.

Brown Recluse Spiders

The brown recluse spider is a venomous spider found in parts of Iowa, primarily along the Missouri border. Identifying features include:

• Uniform brown coloration
• Dark violin-shaped marking on the cephalothorax (body section)
• Three pairs of eyes arranged in a semicircle
• Long, thin legs

Brown recluse spiders build irregular webs in undisturbed areas like attics, crawlspaces, cellars, and sheds. They are usually found in drier areas. Their venom can cause painful blistering and sores if they bite humans.

Controlling Brown Recluse Spiders

To reduce brown recluse populations and prevent bites:

• Seal cracks and crevices where they hide and build webs.
• Reduce clutter and debris where they can hide.
• Vacuum webs and egg sacs.
• Place sticky traps to catch wandering spiders.
• Use insecticides labeled for brown recluse control.

Black Widow Spiders

Black widow spiders are also found in parts of Iowa. Identifying features include:

• Shiny black body and legs
• Prominent red or orange hourglass marking on the underside of the abdomen
• bulbous abdomen

Black widows build tangled webs in protected areas like woodpiles, debris piles, rodent burrows, and crawlspaces. The female's venom is 15 times more potent than a rattlesnake's, but they rarely bite unless provoked.

Controlling Black Widow Spiders

Prevent black widow encounters by:

• Keeping woodpiles and debris far from the home.
• Wearing gloves when moving materials they may hide under.
• Sealing exterior cracks and crevices.
• Checking children's play areas carefully.
• Shaking out shoes, gloves, and equipment stored in garages or sheds.
• Applying insecticides if necessary.

What to Do if Bitten by a Venomous Spider

See a doctor immediately if bitten by a brown recluse or black widow. Quick medical care can greatly improve outcomes. To help with treatment:

• Wash the bite with soap and water if possible.
• Apply a cool compress to the bite area to reduce swelling.
• Avoid physically exerting the bite area.
• Capture or take a photo of the spider for identification if possible.
• Monitor for symptoms of a reaction, including severe pain, nausea, sweating or chills.

With proper precautions and awareness, Iowans can coexist safely with spiders. Their benefits far outweigh the very small risk posed by a few venomous species.

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.