By Laura Jesse
Extension Entomologist
Iowa State University

If you are like me, you have been spending a great deal of time indoors trying to stay warm, and if you also are like me, all this time indoors causes you to start to notice things about your house you may have overlooked before. I personally have been spending a lot of time analyzing the cobwebs I can see from my couch. I should get out the vacuum, but the webs have sort of become part of the décor at this point.

Cobweb is a term we use for messy spider webs in homes, the flimsy webs that sort of drape down and get covered in dust. I am not sure the origin of this term or why we need a separate term for these unattractive spider webs, but it is certain that when someone says their basement is full of cobwebs we know exactly what they mean. For me cobwebs have always seemed a bit mysterious. I rarely see a spider, and yet cobwebs seem to spring up around my house overnight. And once I see one, I start to notice they are everywhere.

There is a group of spiders we call the cobweb spiders, but many species of spiders make messy webs we would call cobwebs. In Iowa the most common species of spider that makes cobweb-like webs is the long-bodied cellar spider. Long-bodied cellar spiders, have a long body (imagine that!) that is usually a bit less than 1/3 of an inch, and very long thin legs that can make the spider seem quite large. The spiders are grayish in color. Sometimes I see long-bodied cellar spiders hanging in their web, but most often I just see the webs. I think this is because the cobwebs do not become obvious until they are old and abandoned by the spider and have gotten covered in dust.

Long-bodied cellar spiders are annoying for leaving what seem to me to be permanent webs in basements, corners of ceilings, walls, book shelves, basically just about anywhere. They are not poisonous to humans and are actually sort of good guys because they eat insect pests, house centipedes, and other things we do not like in our homes. However, at a certain point the ugly dust covered webs are a bit annoying.

Long-bodied cellar spiders would be difficult to eliminate from a home that has a decent population of them, or at least you would have to be a lot more dedicated than I am to controlling them. Often they are concentrated in a dark, seldom disturbed, basement or cellar area. Insecticides are not very effective at controlling them for a few reasons. First off the spiders don't move around that much so the chances of them walking through a residual insecticide are not good; there is probably little exposure to the insecticide from walking through because they are walking on the tips of legs on claw-like tarsi, and finally insecticides are often not as effective as we want because spiders are not insects, they are arachnids.

For cellar spider control the best thing is a vacuum with a hose attachment. Set aside a few hours to systematically move through your house, removing as many webs and spiders as you can. I find it sort of a therapeutic task to vacuum up all the webs from between the floor joists, around the basement lights and windows, and all the other nooks they find. I do feel a bit guilty when sucking up a live spider, but it helps reduce the population. I think if I did this every few weeks I could probably eliminate the population, but usually I ignore them until they get out of hand and start slinging webs across my dirty dishes overnight.

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