You know the old saying: “You can never find a mud dauber when you need one.” Of course you do. Well, the old adage proved itself yet again last week when I went searching for mud dauber wasp nests to photograph.
I’m writing a magazine article on wasps and wanted some photos of various wasp nests to help illustrate it. We have an old garage with lots of great places for mud daubers to build their mud nests, but a thorough search found only a couple empty remnants of very old nests. That’s ok, I had a backup plan.
The Derr House, the field headquarters for our Platte River Prairies, has always been a dependable spot to find nests. Those nests make great discussion subjects with guests. In fact, I’ve told the same story many times:
“Mud daubers are fascinating little creatures. First of all, they don’t attack people, so you don’t have to worry about them. More importantly, a female mud dauber builds a little mud tube on the sides of buildings and other structures. Then, she hunts down and paralyzes some spiders and jams them into the tube. The wasp lays an egg in with the spiders and seals up the hole with mud. The larva can feed on the spiders until it pupates and emerges as an adult.”
Sure enough, when I stopped by the Derr House, I was able to find plenty of mud nests up near the eaves. A couple were extra big, so I figured I’d start by photographing them. They were up high, so I backed my pickup close and set up my tripod on the tailgate. Perfect. Except there was something weird about the mud nest; it had little brown circles all over it. That didn’t seem right.
Well, I was already set up on the tailgate, so I went ahead and photographed the nest, weird circles and all. While I was there, though, I also got curious and decided to investigate a little more. By a strange coincidence, I happened have a couple razor blades in the truck and decided to use one to cut away some mud. It was surprisingly difficult, even with a brand new blade, but I did eventually manage to open the nest a little. What I found was definitely not in line with my story about paralyzed spiders in a mud tube. These tubes appeared to be filled with lots of little leaves.
Well, now I had to keep going and figure what what was inside the leaves, didn’t I? I had a suspicion, but wanted to get photos so I’d be able to confirm or deny my hypothesis. I carved out a part of the mud nest that contained a couple of the leafy cylinders and laid down on the bed of my truck with the cylinders and my camera. I painstakingly peeled the leaves apart on one cylinder… Ok, I tried to, but ended up making a pretty good mess of it. I did eventually manage to figure out that there were multiple hollow sections to the cylinder, each wrapped up tightly in leaves.
Even with the razor blade (somewhat dulled by cutting through hardened mud, of course) it was difficult to slice into those cells to see what was inside. I managed to mangle a couple before finally making a hole big enough to expose a pale larva with little orange spikes on it. Over the next few minutes, I photographed it and a couple of its siblings as they crawled around my tailgate.
After photographing the larvae for a while, I noticed one of the leafy cells had an odd texture on one end of it (below). I photographed it, figuring I could try to decipher it later. I’m glad I did because it became a helpful clue.
As I looked at the remains of the section of mud nest I’d carved off the wall, I noticed something brown had been exposed when the mud cracked. I peeled the mud apart further and finally found what I’d initially set out to photograph – an actual mud dauber pupa. So, this was, in fact, a mud dauber nest. It’s just that it seemed to have a lot of non-mud-daubers in it too. Have you already guessed what they are?
When I got home, I quickly worked up the photos and sent a selection of them to Heather Holm, who (among many other things) knows more about wasps than anyone I know. You might remember the post I wrote a year ago, in which I rhapsodized about her fantastic book on the topic. I asked her to help me interpret what I’d seen, and specifically, if leaf-cutter bees (Megachile sp.) were known to share a nest with mud daubers.
Sure enough, Heather graciously confirmed what I’d guessed. Apparently, at least some leaf cutter bees are known to reuse the holes in mud dauber nests. Heather also agreed that the odd texture I’d seen on one cell was the remains of pollen and a lot of fecal pellets (poop). Wasps don’t provision their nest cells with pollen, so that pretty well confirmed the bee hypothesis.
What’s interesting to me is that it appears that both black-and-yellow mud daubers and leaf cutter bees were using the same structure at the same time. Did the bees move in after the previous year’s wasps had exited their holes? If so, was the wasp pupa an old one that didn’t emerge? That seems unlikely. Surely it would have decomposed by now if it had died, right? Did a black-and-yellow mud dauber reuse a hole from that nest too? Or is the pupa I found actually a blue mud dauber (Chalybion), which is also known to reuse the holes of black-and-yellow mud dauber nests?
The next time I get out to the Derr House, I think I’ll grab a little more of that nest and put it in a jar. Hopefully, I’ll get to see who emerges from all those holes and flesh out this story a little more. I’ll let you know if that works. In the meantime, I need to get this magazine article written…