Entomology (Study of Bugs)/help with ID


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My son was playing in an open space lot next door this afternoon and he discovered these amazing and beautiful spiders. It was shocking how large many of them were, I'm guessing the size of an extra large olive or bigger.  We are just curious about what they are, we would of course like to confirm that they are not dangerous since my son is 10 and will definitely try to pick one up at some point.

To be specific, we live in Moss Beach, Ca  which is about 7 miles north of Half Moon Bay (about 25 minutes south of San Francisco) on the coast. We found them at about 5pm  today 9/15. We just saw one crawling on its web probably because my son jiggled it on accident. Otherwise they were sitting open in their webs or curled up under and overhang of leaves as in the picture.  Sorry they aren't very clear, it was very sunny and hard to find an angle and still focus.

Thank you for any help.

ANSWER: Hi, Joanie:

Thank you for including the images, which are plenty good in the quality department....

The spiders are "Shamrock Orbweavers," Araneus trifolium , and all are female (mature males wander in search of females).  Here's more about them:


These are definitely *not* dangerously venomous to people or pets, so no worries.

I have personally never found this species to be particularly abundant, so I'm intrigued by your finding of so many in one location.


---------- FOLLOW-UP ----------

QUESTION: Thank you so much for the information. It's been great to share this with my son.  In terms of being abundant there very many of them. The space is only just one house lot that has never been built. It's over grown with a high brush and from the naked eye I can see at least 9 of thee spiders, and with a little poking and peering I know there are more like 15 and they are all big.


Thank you for the additional information.  I suspect they are probably all sisters that never dispersed very far from the egg sac their mother laid *last* fall....

I'm under contract to write a new spider field guide for Princeton University Press (will be published in 2016 or so), so I appreciate hearing what "average" people are observing.  Nothing average about *you*, obviously, you are a wonderful mother :-)

Take care.



Entomology (Study of Bugs)

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Eric R. Eaton


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.


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.

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.

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.

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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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