Spiders earn their keep in the garden
September 19, 2015
In corners and along baseboards, on ceilings and spun between shrubs, spiders crawl through our lives this time of year.
“Spiders are on the move right now because they’re looking for a mate,” according to Gail Langellotto, an entomologist with Oregon State University’s Extension Service.
“The domestic house spider is one that regularly makes its way into houses in fall and if you haven’t seen one in the past, it can be a startling sight,” she said. “If you include their legs, they’re about as big as a silver dollar.”
OSU Extension Master Gardeners have been getting questions about whether there are more spiders this year and if they’re bigger, Langellotto said.
“There aren’t more spiders than usual and they aren’t larger,” she said. “Most likely, you’re just seeing a species you haven’t seen in the past.”
Langellotto recognizes the fear some people have toward spiders but points out they have attributes, including their fascinating process of spinning beautiful webs and their predatory nature, which is an important tool in the garden.
“Plus, they’re just cool and awesome,” she said. “They don’t feed on plants; they catch and kill things. They are natural pest controls. I hope people will learn you don’t have to be afraid of them. If you have room in your heart and garden, don’t try to kill them with pesticides.”
Even if you can’t bring yourself to like spiders, keep in mind they aren’t easily killed by pesticides. The amount and concentration needed is often higher than what’s necessary to kill insects, which poses greater risk to humans, Langellotto said. If they’re inside sweep them up and escort them outside. In the garden, just leave them be and they’ll eventually make supper of each other or get eaten by reptiles and birds.
For people who want to encourage spiders – and Langellotto acknowledges that doesn’t apply to everyone – she recommends adding more trees, shrubs and perennials to provide anchor points for web-building spiders to spin their webs.
Spiders spin different types of webs, she said. Some build funnel webs, while others make sheet webs. Some have combs on their hind legs that they use to “back comb” silk and make a messy-looking tangle web.
But it’s the classic orb weavers that people associate with spiders. They dispense strands of silk, which fly through the air, hit something and stick. Then the spider starts to fill in the middle, creating the intricate, lacelike webs that trap prey so efficiently. Although the silk is stronger than steel in terms of mass and more flexible than a rubber band, it’s not difficult to swipe webs away as you walk through the garden.
Of the 700 to 800 species of spiders in Oregon, only the black widow has the potential to cause serious harm to humans. This spider is found in the drier areas of southern Oregon and east of the Cascades more commonly than in the Willamette Valley. Hobo spiders, research shows, are not poisonous to humans, but their bite may cause pain, redness and itching. Poisonous brown recluse spiders do not live in Oregon, according to Langellotto.
Hobo spiders and house spiders (both in the genus Eratigena) look so similar that experts need a microscope to tell them apart. Both are medium brown with a lighter chevron on their upper abdomens. They are usually found in dimly lit areas like boxes, closets, storage areas and woodpiles.
Another common spider, the yellow and black garden spider (Argiope aurantia) can be seen outside where it often sits conspicuously in its orb web in open spaces waiting for prey.
In contrast to the garden spider, black widows (Latrodectus spp.) build messy, mesh-type webs in out-of-the-way spots. Females have a glossy black body with a distinctive red hourglass on the bottom of their rotund abdomens. Male widows are more drab, slender and smaller.
If you’re interested in having a spider identified, bring it into your local OSU Extension office. Make sure the spider is dead; kill them by placing in a container and putting it in the freezer.
“Spiders are not going to seek you out to bite you,” Langellotto said. “The tend to be shy and not aggressive. If you don’t bother them, they won’t bother you.”
If you want to avoid bothering them, here are Langellotto’s recommendations for keeping spiders at bay:
* Wear gloves, pants and a long-sleeved shirt when handling firewood or stored boxes where spiders may have built funnel-shaped nests.
* Seal holes around doors, windows and outlets for plumbing and wiring where spiders can find entry into the house.
* Sweep webs from corners, rock walls and under eaves. Repeat as necessary.
* Keep porch lights switched off as much as possible to keep from attracting flying insects that make good prey for spiders. Or switch to yellow bulbs, which attract fewer night-flying insects.
* Place simple cardboard sticky traps (without the use of insecticide spray) along baseboards and bed frames where wandering spiders tend to move.
* Keep vegetation near house mowed or trimmed.
Photo above by Lynn Ketchum. Garden spiders help out in the garden by eating pesky insects – and other spiders.
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