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Sandy, Utah area (foothill benches. I am seeing sparse (not dense threads or tent-like)spider webs spanning approx 1-2 inches in the crotches of various limbs on scrub oak (no bugs or spiders are visible, however, did recently see only one yellowish/brown spindly pointed legs/body spider on limb which was about 1/2 - 3/4 inch if legs were spread from end to end). I've never seen spider like it before and can't identify on internet or books. Any thoughts, advice, or place to reference on what and how to treat? Scrub overhangs patio and everyone is paranoid to sit under trees. This is only affecting a few trees near pation, not seen on all scrub oak on property.

Answer(s)

A

Can you describe the webs in greater detail?  It would be ideal to
have one of the spiders identify, but if that is not possible don't
worry about it.

Generally speaking I do not like the thought of spiders coming
down on my head either, but I do not think that these spiders will
cause you any harm.  There are only 3 spiders of concern in Utah
(the Hobo, black widow, and yellow sac spider),and that doesn't
sound like any of them. You probably already know what a black
widow and a hobo look like... In terms of the yellow sac spider,
what you have described doesn't sound like their usual behavior.
Here is a picture of a yellow sac spider:
http://bugguide.net/node/view/41792/bgpage
When bitten by one of these your body usually reacts the same
as if you were bitten by a mosquito.  In severe cases some localized
skin necrosis might ensue. People in Utah are probably most commonly
bitten by these spiders in their home.

If you are actively looking for spiders and can't find any, then
they are likely not a problem.  I would consider their webs
a benefit as they may be catching mosquitoes, gnats, etc. If you
want to do something about the webs I would recommend spraying
them out of the tree with a hose.  If you do this enough it may
deter the spiders from building webs, and may drive them off
to other trees to inhabit.

Please let me know if you want more information and I will get
back to you ASAP.

Posted on 6 Aug 2008

Ryan Davis
Arthropod Diagnostician, Utah Plant Pest Diagnostic Laboratory

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