Thursday, September 19, 2013

The Spiders and the Cat

Posted by: Susan Rose, Tri-River Area Extension

Grand Junction - This summer, Dr. Whitney Cranshaw was seeking volunteers on the western slope to put out sticky traps to monitor indoor spiders. He's working on a paper on them in Colorado, and wanted some data over here to supplement what he already has for the Front Range.  As I live in a 104 year old house in downtown Grand Junction which is definitely not spider-proof, I offered to set some traps.

While the spiders basically ignored the traps, the project gave me some opportunity for observation and reflection.

When we moved to Grand Junction in 1975, the old family house had been empty for several months.  We discovered a healthy population of widow spiders (probably Latrodectus hesperus, the western widow) especially in the basement - a matter of concern with a five-year-old child.  A couple of years later though, the cellar spiders (Pholcidae) moved in and within a few years we saw a significant decline in the widow population.

I thought this might be a case of competition, as the widows basically park, and the cellar spiders are highly mobile and appear to cover large territories.  In a discussion with Whitney about this, he thought the answer might be a bit more straightforward: the cellar spiders' diet consists primarily of other spiders, which they actively hunt.  Whatever the reason, the result appeared pretty positive to me and I decided to tolerate a small permanent herd of the long-legged good guys.

Miss Molly...the spider huntress
Enter Miss Molly, stage right.  My six year old brown-point Himalayan kittie fancies herself a mighty huntress but since she's strictly an indoor girl she doesn't get a lot of opportunities.  She has shredded the front porch screen climbing after pigeons and necessitating the purchase of the more expensive "pet screen" which she now disdains to climb.  It's currently open season on field crickets (the house definitely isn't cricket-proof either) to her great delight, but for most of the year all she has to chase are those spiders.

Slowly over the last several years, there has been another population shift and while the cellar spiders still predominate, I am seeing fewer of them and more of the widows.  In fact, I had a rather too close encounter with one a couple months ago, though Bob Hammon, Tri River Area's wonderful entomologist, was skeptical.  I reached my conclusion based on the tell-tale double puncture wound, the amount of swelling and pain, and the duration of the truly infernal itch.  And, oh yes, the dead spider in my bed where I had apparently rolled over on her.  I wouldn't wish this experience on anyone, except maybe for skeptical entomologists (just so you'd really know!)

I don't know for certain that Miss Molly (yes, I confess, she was named for the old song) has effected this population shift, but it's what I suspect.  It's that mobility of the cellar spiders - they frequently do come within three feet of the floor where they are fair game.  She'd rather play with them than eat them, but they rarely survive her attentions and the result seems to be this slow alteration in the spider ecology at the Rose residence.  

It's a little early for a Hallowe'en story, but I found it pretty interesting and would like to hear your thoughts.

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