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Entomology (Study of Bugs)/What kind of spider is this?

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Question
Spider
Spider  
Hi Eric.  Please see the attached pic.  I have found many of these spiders in my backyard in Dixon, Illinois near the Rock River.  This picture was taken on 6-3-2013.  The spider is brownish in color and has a black lung-shaped mark on its underbelly.  It is about as big as a half dollar coin, including its legs, and makes a tangled web. Its body has about the same diameter as a nickel.  Any help would be appreciated.  I'd like to know what it is and if it is venomous.  -MissDaisy

Answer
Hi, again :-)

The spider is clearly an orb weaver, family Araneidae.  The only common species that are that large and in the adult stage at this time of year are the "furrow orbweavers" in the genus Larinioides :

http://bugguide.net/node/view/33791

No orb weaver of *any* species is known by science to be dangerously venomous to people or pets.  Indeed, they are important agents of pest control, trapping hundreds of thousands of mosquitoes, midges, moths, and other insects in their webs.

Furrow orbweavers are in their webs almost exclusively at night.  I have found the webs during the day but have seldom seen the spiders, so well do they hide.

Eric

Entomology (Study of Bugs)

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Eric R. Eaton

Expertise

I answer insect and spider identification questions ONLY. Attach images if possible. No "what bit me?", "what do I feed this bug in captivity?", or science fair project questions please. NO TECHNICAL QUESTIONS ABOUT INSECT PHYSIOLOGY.

Experience

Principal author, Kaufman Field Guide to Insects of North America. Professional entomologist employed previously at University of Massachusetts, Chase Studio, Inc., and Cincinnati Zoo; contract work for West Virginia Department of Natural Resources, Smithsonian Institution, and Portland (Oregon) State University.

Publications
Author, Kaufman Field Guide to Insects of North America, Missouri Conservationist magazine, Ranger Rick, Birds & Blooms, Timeline (journal of the Ohio Historical Society). I have contributed to several books as well.

Education/Credentials
Oregon State University, undergraduate major in entomology, did not receive degree.

Awards and Honors
One of the top 50 experts in all categories for AllExperts.com, 2009.

Past/Present Clients
Principal author of the Kaufman Field Guide to Insects of North America, Smithsonian Institution (contract), Cincinnati Zoo (employer), Portland State University (contract), Chase Studio, Inc (employer), Arkansas Museum of Discovery (guest speaker). Currently seeking speaking engagements, leadership roles at nature festivals, workshops, and ecotours.

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