Deadly Digger Wasps

Last January, plumbers installed a new drainfield for my septic tank, reducing my wealth by about $5,000.  The alternative was a monthly $200 bill to pump out a tank that had become clogged with biofilm which is just a fancy word for shit turned into mud and root masses.  They had to dig up a significant wedge of my backyard, felling a productive fig tree in the process.    They covered the new pipes with bare dirt, and I transplanted a few peach tree saplings in the empty space.  I don’t care for well manicured lawns–the boring landscape choice of most of today’s fascistic conformists. So I didn’t plant any grass.  Instead, I looked forward to seeing what plants existed in the natural seedbank, though I did plant a few rows of oats and fieldpeas and scattered a container of wild flower seeds in 1 patch.  Now, there is a nice carpet of crabgrass, nutsedge, and wild sorrel growing underneath the pokeweed (aka pigeonberry) and nightshade I choose to let stand when I swing the scythe I use to keep my yard from looking so unkempt that I get yet another city code violation.  There are still patches of hard packed sand in this miniature wilderness, and these bare spaces attract female digger wasps.

Cerceris bicornuta , the weevil wasp, digs a chamber into hard packed sand where it lays its eggs.  It then goes hunting for weevils.  It subdues the weevils with paralyzing stings and deposits them next to its eggs.  The paralyzed weevils stay alive and fresh and become food for the wasp larva when they advance past the egg stage.  I found a weevil wasp in my yard, and one evening I placed a glass jar over its chamber entrance in the hopes that I’d get a good look at it, but alas it had evidentally abandoned the nest.  Nevertheless, the below photo is a much better image than I could have gotten with my cheap camera.

Female Cerceris bicornuta on Virginia Mountain Mint

Adult weevil wasps get energy from the sugar in flower nectar, but they have an all protein diet in their larval stage.

The weevil wasp belongs to the Crabronidae family which includes 200 genera and over 9000 species.  Most of the species in this family dig chambers into the ground, though some build nests elevated above ground.  Most wasps in the Cerceris genus are specialized predators of weevils.  The Astata genus includes predators of stinkbugs, the Zyzzyx genus includes predators of flies and butterflies, the Sphecus genus are known as cicada killers, the Pison genus are murderers of spiders, the Microstigrinus genus are social wasps  preying on everything from flies to caterpillars, and the Philanthus genus slaughters bees.  Digger wasps are deadly to whatever prey they specialize in feeding to their larva, but not to humans, unless a particular individual suffers from the type of allergy that causes an extreme auto-immune response.

Today, diggers wasps benefit from human construction activities that create bare patches of hardpacked sand such as dirt road sides or cleared land where they can dig their nesting chambers.  During the Pleistocene, digger wasps likely benefited from the presence of large congregating herds of megafauna that trampled and denuded vegetation, creating the ideal bare surfaces they require to nest.  Digger wasps have existed for at least 300 million years and shared planet earth with the dinosaurs.  But most people view diggers wasps as minor annoyances with the potential to sting.  Wasps do not exist simply to sting people.  They play a central role in controlling populations of insects that may actually compete with humans for survival, as any gardener or farmer plagued with stinkbugs, flies, and aphids can understand.  They deserve our respect for they will probably still be digging nesting chambers in bare patches of earth long after Homo sapiens suffers extinction.


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