Pipe Organ Mud Dauber Wasp and Parasitic Fly

About two weeks ago, while sitting on the front porch cleaning my boots, I heard the unmistakable buzz of a female Pipe Organ Mud Dauber, Trypoxylon politum, sealing up a brood chamber inside her nest. This species of wasp uses mud to construct a long tube which it divides into individual compartments, each of which will be loaded with a collection of venom paralyzed spiders to be used as a food source for a developing wasp larva. I looked over and saw that the female wasp was in the process of sealing off the bottom chamber of a long tube nest.

I was not the only one interested in this activity. A female Tachinid fly was stalking around the entrance to the nest, waiting for an opportunity to sneak in and leave one or two of its eggs inside the brood chamber. Gaining access was not an easy process. While the female wasp was away gathering more mud, the male wasp moved in to guard the nest entrance.

Eventually, as the female wasp put the finishing touches on the bottom seal of the brood chamber, the male wasp moved away and allowed the fly to slip in.

The video above shows the female wasp bringing in mud to seal the last brood chamber, the male wasp performing its guard duty and attending to the female, and the fly skirting around the entrance to the nest and finally seizing its opportunity to enter. A longer version of this video can be seen on YouTube by clicking HERE.

Yesterday I spotted this fly resting on the outside of the tube nest. It was obviously freshly emerged and its appearance was marred only by a few crumbs of dry soil matching the color of the nest.

Not far away from the fly was the hole through which it had escaped the wasp brood chamber.

I scraped a bit of soil away from the site of the exit hole and discovered the empty pupal case left behind by the fly.

Further excavation revealed what was left of several spider carcasses and what looked to be additional fly pupae.

Here’s what was inside the chamber. There was evidence of three Tachinid fly pupae.  The larvae had feasted on the spiders, leaving only empty husks behind.

Two pupae were intact, containing flies that would probably soon be emerging. A single empty case was left by the fly I had observed earlier.

Pipe Organ Mud Daubers frequently construct their nests on my porch. Some of the holes in this nest from last season were probably made by emerging wasps, but I know that several were made by foraging woodpeckers.

Closer examination of the old nest reveals smaller holes that are just the right size for an emerging fly. I imagine this fly and wasp a game is a common occurrence on my front porch.