AMES — It’s been hot and dry for weeks and many Iowans who haven’t mowed their grass in a while are finding little patches of what looks like white cotton candy strewn around their yards. Ginny Mitchell, an entomologist at Iowa State University, says those are the webs of grass spiders and there are easily hundreds of species of the tiny arachnids.
Don’t fear an invasion, as Mitchell emphasizes, they’re good bugs. “They’re very beneficial because they’re eating the plant pests that would otherwise devour the plants — including grass — that are in your yard,” Mitchell says. “So when you see lots of those spider webs covering your lawn, that’s actually a good sign. That tells you those spiders are eating other insects so that it can reduce the number of pests in the environment.”
Mitchell, who’s the Education Program Coordinator of ISU’s Insect Zoo, explains why there are so many webs in our yards, perhaps dozens. “There must have been a really good egg sac that hatched in the area,” Mitchell says, “and then there’s so much food that all of the siblings did not feel like that was not a good place to live, and so they set up shop close to home.”
Eventually, we’ll have to mow again, which will ruin all of those carefully crafted webs, but that’s the cycle of life. Mitchell says don’t feel sorry for the spiders, as they will feel the vibrations of the approaching lawn mower long before it reaches their sticky lairs. “So as you are making your way through your yard with your lawn mower, those spiders are going to know that something is going on and they’re going to run down for cover,” Mitchell says. “They will be protected, so don’t feel bad. Also, they are really good web builders, so while you may have destroyed their web by mowing, they’re going to come back and they’re going to rebuild that web.”
As fall arrives and the weather cools, some of those grass spiders may try to find a way into your house. Mitchell says to let them be, as they’re gobbling up -other- unwanted pests. The rest of the spiders will stay in the yard and many will make it through the frigid months ahead. “The majority of the females that are in your yard right now will spend the winter in leaf litter, which is why it’s important to leave your leaves in the fall,” Mitchell says. “In Iowa, that’s where the bugs over-winter. It’s really warm down there because of the decomposition that’s happening, so it creates heat and so that’s where the bugs stay warm.”
The grass spider webs are typically strung between the tips of grass blades, and you may spy a small funnel or entrance hole in the web. Mitchell notes there’s a fungus that can grow on grass, called dollar spot, which may look similar to the webs, but the fungus will also be down towards the roots.