The common house spider is the most commonly encountered species of spider in the home. The house spider is relatively small, with a body size of less than .25 inches. House spiders are a dull, brown color and have spotted patterns along the legs. House spiders are not aggressive and are acclimated to human presence. They bite only in extreme cases of self-defense. They feed on flies, mosquitoes and other household pests.
The jumping spider family is the largest group of spiders in the world. They are commonly found on the walls of homes, as they hunt to capture prey. Jumping spiders cannot leap more than a few inches, and the varieties found in northern Illinois are relatively small. The spiders feed on flies and other insects they can capture. Jumping spiders have colorful markings on the abdomen and are not poisonous, though they may bite if threatened.
Yellow Sac Spider
The yellow sac spider is usually a pale yellow or green. They generally build webs in ceiling corners or the joints between walls. The yellow sac spider is the most aggressive species of spider in the Chicagoland area, and most bites occur when the spider crawls into clothing or bedsheets. A yellow sac spider bite results in a burning sensation, redness and swelling at the site.
The cellar spider is another commonly encountered spider throughout northern Illinois. They are found in cellars, basements and other damp areas. Cellar spiders can have legs up to 2 inches long. They feed on other spiders, mosquitoes and even their own species when faced with starvation. Cellar spiders are harmless to humans, and their primary defense mechanism is shaking their web violently when threatened.
Brown Recluse and Black Widow
The brown recluse and black widow spiders reside primarily in southern and central Illinois, though bites from both species have been reported in Chicago and northern Illinois. Brown recluse spiders have a distinctive violin shape on their back and six eyes. They are highly poisonous and can cause necrosis of the flesh or death if the bite is left untreated. The northern black widow spider is also found throughout Illinois. Black widow spiders are distinguished by a red hourglass on the abdomen. Their bite, especially from female spiders, is extremely poisonous to humans.