Spiders in a mud nest

Asked July 30, 2017, 6:53 PM EDT

I found what looked like a wasp nest on a patio umbrella. When the mud nest broke apart there were these spiders in there with larva in it. See picture. There are about 20 or more spiders. What are they and why we're they in the mud nest.

Johnston County North Carolina

2 Responses

Thank you for your question. I apologize for the long delay, but your question has been moving around from expert to expert to try to get you an answer. I suspect I know what's going on, but want to check with an arachnologist contact. I'll be back in touch with you as soon as I hear from them.

Thank you for your patience.

Jim

Hello again. I heard from an arachnologist contact I have at the University of Missouri. He knew exactly what was going on with your spiders as soon as he saw the photograph.

Female mud daubers construct tubular chambers constructed from balls of clay that they collect from areas of moist soil or clay. She uses her legs and jaws to form a ball of mud and then carries it back to the area where she has chosen to build her nest. Usually on a protected wall under an eave, on barn rafters, or, in your case, your patio umbrella. She continues to gather balls of clay or soil and pack them together until she has formed a tubular chamber.

At this point, she goes in search of spiders to supply her nest. She will find a spider and sting it. The sting paralyzes, but does not kill the spider. The mud dauber then carries the live spider back to her nest and places it in the nest chamber. The female will do this repeatedly until she has a dozen or so paralyzed spiders packed into her single chamber. At this time, she lays a single egg in the chamber and collects more mud/clay and seals the chamber. The mud dauber egg hatches and the larva, or grub, crawls around until it finds the first spider. It bites the spider, which is still alive, near its waist and begins sucking out the spiders fluids and internal organs - the heart and nervous system are the last organs to be consumed. Then the grub moves to the next spider and continues to feed. By the time the larva has consumed all or most of the spiders, it has has molted several times and significantly increased in size. At this point, the larva pupates and develops into an adult mud dauber, chews through the clay sealing the nest chamber and starts the cycle all over again.

It can be difficult to identify spiders and insects, based on photographs, because you usually can't see the distinguishing characteristics necessary to make a positive identification. However, the spiders in your photograph look like marbled orbweavers (Araneus marmoreus).

Here's a site that provides additional information on mud daubers:
https://en.wikipedia.org/wiki/Mud_dauber

and here's a site with additional information on the marbled orbweaver:
http://ento.psu.edu/extension/factsheets/marbled-orbweaver

Hope this answers your question, and thank you for contacting Ask an Expert.

Jim