Poisonous Spiders in Iowa

Among all the species of spiders found in Iowa gardens, only two, the brown recluse and the black widow, possess venom strong enough to pose a serious health threat to humans. Both of these spiders are rare in the state, however, and their bites do not very often cause life-threatening reactions.

The brown recluse is a medium-size spider, with a body length of about 3/8 inch and 3/4-inch-long legs. It is usually light- or medium-brown and often has a violin-shaped marking on its back, although the marking is indistinct in some specimens. As its name implies, it is a reclusive spider, and it typically is active only at night. During the day, it hides in secluded areas, such as under rocks and logs, in piles of wood and brush, and in garden sheds.

The bite of the brown recluse is very often not painful at the time of the bite, but the bite area usually begins to sting or burn within one hour. The area may become red, swollen and hot within a few hours, and a small blister develops at the site. Over days or weeks, an open sore or a blackened area of dead tissue may develop around the bite.

The brown recluse is most common in the southern United States, but its natural range extends into southern Iowa. The species is rare in the state, however, and it is unlikely to survive outdoors in the northern part of the state.

The black widow spider is the only other species in Iowa that poses a serious threat to people. The venom of a female black widow contains a toxin that can cause muscle cramps, nausea and vomiting, fever, headache and shortness of breath. In children, elderly and individuals with compromised health, the bite may be fatal.

The female black widow is about 1/2 inch in body length and about 1 1/2 inches wide with its legs extended. It is shiny black and usually has a red hourglass-shaped marking on its belly, the underside of its abdomen. A male black widow spider is considerably smaller, and its bite is not dangerous.

The female black widow lives in quiet areas, such as in woodpiles and under low foliage. There it constructs a messy web in which it lays its eggs in egg cases. The spider almost always remains in the web and guards the eggs, and it may bite to protect them and itself.

Appropriate immediate treatment for all spider bites includes applying ice to the site of the bite to reduce swelling.

In the case of a suspected black widow bite, get medical attention as soon as possible. Treatment at a medical facility may include the monitoring of your condition and administration of medication to treat pain. In extreme cases, administration of anitvenin may be required.

Seek medical attention for a suspected brown recluse bite if an open sore or sign of infection develops, or if you develop symptoms beyond those at the bite site.

Keeping your yard and buildings uncluttered, as well as removing debris, brush piles and other spider habitats, will help to keep the spiders out of your property.

When you work in or near potential spider habitats, wear gloves, a long-sleeved shirt and long pants, and don't reach under foliage, logs or brush piles if you can't see where you're reaching.