NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665


September 7, 2000

Spiders Plentiful and Visible in Fall

Late in the summer, spiders tend to be at their peak in both population and size. Webs are plentiful, so people notice them and may think some kind of spider population explosion is under way.

According to Phil Glogoza, extension entomologist at North Dakota State University, spiders are beneficial predators feeding mainly on insects, including many pest species. All spiders are venomous, but most are harmless to people. They are not aggressive, and few will bite. If they do bite, the bites of most spiders are less painful than a bee sting.

Spiders can be found indoors any time of year but numbers usually peak in late summer or fall. Glogoza says it would be difficult to eradicate spiders from around a home, but it is also unnecessary. Spiders are beneficial to the environment and should be tolerated if possible, he says.

If it is necessary to reduce the number of spiders around the home, Glogoza recommends starting with measures to prevent them from entering the house, including removing debris that may harbor spiders, keeping grass and weeds cut short, and trimming back trees or shrubs that contact the house. Caulk or seal cracks, replace damaged screens, and remove webs, egg sacs or spiders that are found. Indoors, clean regularly to reduce insect populations that may attract and sustain spiders. Cleaning regularly in corners and undisturbed areas prevents spiders from finding a safe refuge.

Use insecticides only after trying nonchemical methods, he says. Common pesticides available to homeowners include diazinon, Dursban and permethrin. Use any pesticides only as stated on the label.

Spiders can be divided into two groups, hunting spiders and web-building spiders, depending on how they capture their prey. All spiders produce silk, but hunting spiders do not build webs to capture food. Web-building spiders live in or near their webs and wait for food to come to them.

Common hunting spiders in North Dakota include the jumping spiders, wolf spiders, sac spiders and crab spiders. Jumping spiders are medium sized and dark colored with white or bright colored spots. Wolf spiders are large, dark gray or brown with white markings. Sac spiders are small, yellow to light colored, and can often be found hiding in a rolled up leaf. Crab spiders are small to medium size, ranging from yellow to red to brown color. Their first four legs are long and crab-like.

Common web-building spiders include house spiders, barn spiders or orb weavers, and grass spiders. House spiders are small to medium sized, brown to gray, and build webs in undisturbed areas, indoors and outdoors. Barn spiders are most commonly found outdoors, have swollen-looking abdomens, and construct the familiar round, wheel-like webs. Grass spiders are common outdoors, medium sized, brown to gray colored, with dark stripes. Their webs are large flat sheets with a funnel for a retreat.

The black widow and brown recluse spiders, whose bites are potentially dangerous, are not native to North Dakota but may occasionally be found in the region, Glogoza says. Young black widow spiders are sometimes blown in by storm fronts. Brown recluse spiders may be transported to the area in shipments from southern or midwestern states.

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Source: Phil Glogoza, (701) 231-7581
Editor: Gary Moran, (701) 231-7865