Thursday, July 22, 2010

Black-and-yellow Mud Dauber

Black-and-yellow Mud Dauber, Sceliphron caementarium, hunting the leaves of Prairie Cord Grass, Spartina pectinata.

I had the great fortune to cross paths with one of our most spectacular wasps the other day. Black-and yellow Mud Daubers are big, charismatic, and incredibly showy. And total bad**ses to boot!

Many people know the mud daubers by their distinctive adobe nests plastered under eaves and elsewhere on buildings, bridges and other structures. Far fewer probably get to - or want to! - observe them hunting. But hunt they do, at least the females, and that's what the one above is doing. I apologize for the somewhat fuzzy photos, but when in pursuit of prey, mud daubers are in constant motion and it is work to hang with them and get a perfect shot.

This is a striking insect, with its gloss-black abdomen and thorax set off by bright yellow legs and hash marks on the thorax. The bulbous abdomen is connected to the rest of the insect by an impossibly slender petiolate extension; this bug is truly wasp-waisted!

So, what do Black-and-yellow Mud Daubers hunt? Spiders! I told you, these wasps are true tough guys; the terminators of the insect world. Chances are, you scream and shout if you find a spider in your house. Mud daubers look for them. Wasps in spider-hunting mode are a marvel to watch, as they methodically scurry through the vegetation, often walking upside down under the leaves as that's where spiders sometimes hide.

Some spider-hunting wasps seem to work the ground primarily, looking for wolf spiders. Others, such as this one, seem to go after the more arboreal spider species and are more often found hunting in foliage.

It seems somewhat extraordinary that a wasp would confront and attack a spider, and often species that are quite large. In reality, I suspect the spider doesn't even have a chance. I once saw a ground-burrowing spider wasp, Entypus unifasciatus, take out a big wolf spider right in front of my eyes. I don't think the spider even knew what hit it, so rapidly did the wasp move.
Nursery Web Spider, Pisaurina mira, probably a common prey item for Black-and-yellow Mud Daubers, as this spider frequents low-growing plants and is common.

So, what does the wasp do with the spider? Eat it? Well, yes and no. To be a spider and successfully be bagged by a mud dauber is truly a fate worse than death. When the dauber encounters a suitable spider, it is on it fast as a wink, and jabs the victim with a formidable stinger. Like a hypodermic explosion, it pumps a strong neurotoxin into the spider, which almost instantly disables it. Within seconds, if that, our spider is rendered immobile.

The wasp - quite a powerful brute! - then airlifts its prey back to the nest.
Photo: Tim Daniel, Ohio Division of Wildlife.

Pipe Organ Mud Dauber nest. Black-and-yellow Mud Dauber nests are somewhat similar but more globular, and used for the same purpose. In the above photo, part of the nest has been rasped open, exposing the crypt chambers within. Each chamber is provisioned with spiders - paralyzed spiders. Once Mrs. Dauber has filled a crypt, she lays an egg inside and seals it. When Junior hatches, the wasp grub is assured of fresh meat to feast upon.

Mud daubers have their own worries, though. A number of other species of insects, including a cuckoo wasp, attempt to slip into the nest undetected and lay their eggs within. If successful, the parasite's eggs will hatch first and it will feast on the crypt's contents, including apparently the egg or grub of the dauber.

But if all goes well, a gorgeous, big black and yellow wasp will emerge, the end product of what is certainly one of the oddest, most ghoulish life cycles in nature.

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2 comments:

OpposableChums said...

Fascinating...

Saw my first one last summer. Great to have some insight into what it was doing. Thanks.

Anonymous said...

I saw one today for the first time; this has lead to spending the last couple hours on the web researching them and making fascinating discoveries about this marvel of a creature!

One particular curiosity that remains unanswered for me: What function does the petiolate extension between the 2 abdomens serve?