Murder Mystery in the Spider House

It was a warm, sunny day in the outskirts of the city. The windows were open and the sheer curtains were billowing in the breeze. The day was lazy with the cats perched on the window sills, ears and tails twitching. I was digging around in my supplies when I heard the strangest sound. It sounded like a miniature buzz saw coming from under a fold in the lace fabric which was draped around the door frame. As I started to pinpoint where the sound was coming from, a black and yellow, thread-waisted wasp, rushed out from the fabric and beelined out through an unscreened window. The wasp wasn’t large, maybe slightly over an inch long, and mostly black with touches of yellow at the ends of her thorax and abdomen. Under the lace fold was the beginning of a tube-shaped, mud nest – a tomb meant specifically for spiders.

Within a few minutes, the wasp returned. Her flight was direct as she landed following the fold up to her unfinished nest and began buzzing busily. The wasp carried enough mud to add a few millimeters to the nest in a back and forth motion using her mouth. Check out the video. After about one minute of adding more mud and making that mechanical buzzing sound, the wasp scrambled down and flew out of the window to retrieve more. Sometimes, she’d miss the opening, fly back towards the nest, and then try again which showed that she was visually orienting herself using landmarks, which was pretty cool. A few times, one of the cats noticed and even took a swat at her as she sped by. It took her about an hour and many back and forth trips to complete one mud tube. I had seen this kind of thing before and wrote about it in Spider Horror Stories (from the spider’s perspective). The modus operandi of this wasp is to build a mud nest, hunt spiders by paralyzing them with a sting, and then seal the defenseless spider in the nest with dozens of other paralyzed spiders. The spiders provide food for the larvae. There is usually more than one tube/tomb plastered together if the area is left undisturbed. I observed her for a few days and knew she was hunting when the nest was not capped. At night, she’d seal it off to keep it free of parasites and then disappear outside somewhere until the next day.

One morning, I heard her noisily “saw off” the cap, which gently tapped to the floor meaning she was ready for more spider victims. I couldn’t believe this was happening inside the spider lab, inside the house, just ten feet away from the spiders I was keeping! The wasp completely ignored (or didn’t even sense) the spiders just ten feet away and even if she did sense them, they were protected in their enclosures.

The spider lover in me wanted to derail the whole thing and spare the eventual casualties, but my curiosity took over. I knew the nest was full when it was capped and she returned to the same spot to begin making a second nest. I pulled the first tube off of the lace while she was in mid mud run. The wasp didn’t seem to notice the other nest was gone and she was just as focused on construction as the first time. I carefully broke open the mud tomb to find eighteen paralyzed spiders, a wasp larvae, and two spider heads (with legs). The spiders were mostly orb weavers in the Araneidae family and crab spiders from the Philodromidae and Thomisidae families. I began to profile the killer by searching for more info on what kind of wasp I was dealing with – specifically, since a number of wasps share this behavior.

After reading studies that referenced more studies to even more studies on this interesting topic (mud daubers and spiders as prey has been very well documented), I was able to come up with a few suspects. One is Sceliphron caementarium, the black and yellow mud dauber. She fit the profile. She had yellow markings, made cylindrical mud nests, and focused on hunting spiders. Another suspect would be Chalybion californicum, whom did not fit the profile being a metallic blue and without any yellow at all. It wasn’t a pipe organ wasp, Trypoxylon politum. The color, body shape and nest shape didn’t match.

One night, I noticed the second nest had not been capped and wondered if the wasp had, herself, succumbed to some sort of ill fate. I was hoping to eventually capture her and get some photos to confirm her identity. Then, I thought I found her! There was a wasp in the bedroom window trying to get out through the screen. I captured it in a small container and used CO2 to anesthetize it, but the CO2 proved to be fatal. I may have killed the killer. And I’m guessing my accomplice was one of the cats on guard at the window. Maybe they swatted the wasp off track and she went into the wrong room. The wasp, although it had the threadlike abdomen, did not look like the wasp that was building the nests. There were no yellow markings.

Coincidence? Maybe. The mom wasp never did return to the nest. But the profiles just didn’t match! I opened the uncapped second nest for more clues assuming mom wasp was not returning. Inside was a larvae and nine spiders. I recognized some of the spiders, but never saw them around the house or in the neighborhood for that matter. Where was the wasp hunting? I realized how morbidly convenient this was. I had spiders delivered to me that remained motionless indefinitely so I could get them under the scope for ID!

 

 

After clearing my desk (labeling, storing, and wrapping up notes) I was left with twenty nine spider corpses, one unidentified wasp body, two dried out wasp larva, and two cats who were very tight-lipped about anything they may have seen or heard (or swatted). Then, just when I thought I had all the info I could attain, above the door of the crime scene were two spiders trying their best to camouflage themselves against the white wall. Survivors! They HAD to have come from the nest. Verrucosa arenata is a forest dweller, not the kind of spider that is found in homes. Plus, I had identified the bodies of at least three Verrucosa arenata from nest two. I read that the sting of a mud dauber wasp irreversibly paralyzes the spider. How was this pair, a mature male and female, alive?

 

Left with more questions than I started with, I have to chalk this up to a cold case. The time it’s going to take to follow up on the research that already has been done identifying mud daubers, looking up work on the effects of their venom to see if anyone else had survivors in any experiments, and reading through the awesome 600+ page book, Sphecid Wasps of the World would only further delay the publishing of this post. I shall leave a few blank pages in my notebook as new evidence becomes available.

For every mystery, someone, somewhere knows the truth. Perhaps that someone is reading. Perhaps that someone is you!

Sources: Bohart RM, AS Menke. 1976. Sphecid wasps of the world. A generic revision. Berkeley, CA: Univ. of California Press

Blackledge, T. A. & Pickett, K. M. 2000: Predatory interactions between mud-dauber
wasps (Hymenoptera, Sphecidae) and Argiope (Araneae, Araneidae) in captivity.
J. Arachnol. 28, 211-216.

Muma, M.H. & W.F. Jeffers. 1945. Studies of the spider prey of several mud-dauber wasps. Ann. Entomol. Soc. America, 38:245–255.

Horner. N. V., and 1. H. Klein. Jr. 1979. Spider prey of two mud dauber wasp species in Comanche County, Oklahoma (Hymenoptera: Sphecidae). Environ. Entomol. 8:30-31.

O’Brien, Mark F. (1989) “Distribution and Biology of the Sphecine Wasps of Michigan (Hymenoptera: Sphecidae: Sphecinae),” The Great Lakes Entomologist: Vol. 22 : No. 4 , Article 2. Available at: http://scholar.valpo.edu/tgle/vol22/iss4/2

Powell, E. and Taylor, L.. (2016, May). Featured Creature – common name: black and yellow mud dauber, scientific name: Sceliphron caementarium (Drury, 1773) (Insecta: Hymenoptera: Sphecidae) Retrieved from http://entnemdept.ufl.edu/creatures/MISC/WASPS/Sceliphron_caementarium.htm

Powell, Erin C, and Lisa A Taylor. “Specialists and generalists coexist within a population of spider-hunting mud dauber wasps.” Behavioral ecology : official journal of the International Society for Behavioral Ecology vol. 28,3 (2017): 890-898.