Spiders Are Beneficial.

By Penny Pawl, UC Master Gardener of Napa County

Although the nursery rhyme tells us that Little Miss Muffet was frightened by them, spiders are in fact beneficial insects. 

Scientifically speaking, spiders are Arachnids, invertebrates with two body segments, eight legs, no wings or antennae and no ability to chew.

I have several daddy long legs living in my house right now.  We coexist well.  They make large, messy webs on my ceilings.  As soon as I clean up their webs, the spiders go right back to work.  They make their webs in my garage also.  I seldom find them outside. 

The world of spiders is a big one.  There are thousands of different types in California.  Among the most common are tarantulas, grass spiders, Calisoga [sic] spiders, daddy long legs, sow-bug killers, American house spiders, black widow spiders, wolf spiders, garden spiders, and jumping spiders.

Occasionally you hear of someone getting bitten by a brown recluse spider, but those spiders are not established in California.  When people move around the country, they can unknowingly bring them into California on household items.

About 20 years ago, I was bitten on the wrist by a spider found in linens that had recently arrived from another state.  The bite was very painful, and the spider looked suspiciously like a brown recluse, but I squashed it so could not get it identified.  If you get bitten by a spider and think it might be a brown recluse, seek immediate medical attention as the flesh around the bite slowly rots away.

Among all these spiders, we seem to hear the most about black widows.  They will bite and their bite is poisonous.  A black widow lived for a few years in a corner of one of my worm bins.  We showed respect for each other and she never attacked me.  When I worked in the bin, she moved to the corner and I avoided her.

The house spiders in my home are mostly daddy long legs; they are also called cellar spiders.   They are easily distinguished by their exceptionally long legs, as compared to the size of their body. They belong to the Pholcidae family, which has about 80 genera and 1000 species.

A day or two ago I noticed a tiny thin web in my kitchen window. I searched around the window and, yes, the daddy long legs was back. Sometimes I wonder if it ever leaves. I have vacuumed the web up but somehow the spider survives.    

According to what I have read, these creatures love to live with humans. And they like areas where there is some dampness. They do possess some venom, but their little fangs are not long enough to pierce human skin.

Rather than bite their prey they roll the prey up in their web. If you look at the web, you will see little bundles stored here and there. They have the messiest webs of all spiders. Unlike the neat webs so many spiders spin, these are just pieces of silk going every which way. The spiders usually hang upside down in their web, just waiting for something to become entangled. This habit, along with their legs, makes them easy to identify.

On occasion, and as recommended by the UC Davis Integrated Pest Management (IPM), I have moved other types of spiders outside. Most spiders are great at pest management. It is estimated that spiders eat 800 million tons of bugs a year. Most of their prey are flying insects, although at times they will target non-flying insects.

While researching this article, I learned that Pholcids feed on house spiders and keep flies in check, so your house will be cleaner if you leave them in peace. If you see a spider, you don't need to remove it. Just remove the messy web on occasion.

The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening or upcoming programs, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed but we are answering questions remotely and by email. Send your gardening questions to mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.  

UC IPM has this Pest Note on spiders, with identification guidelines, and management advice.

http://ipm.ucanr.edu/PMG/PESTNOTES/pn7442.html