Top Photo: Sand wasp hovers above concealed burrow.
I just assumed the sand wasps I was looking at were Bembix species of wasps. The wasps were buzzing low over sections of the large, empty sandbox area of Gateway Park which has been closed since the start of the Pandemic (I’ve been told the area will re-open in the near future, but until that time it’s home to various insects including the always fun to watch sand wasps).
The 20 some North American species of solitary wasps known as Bembix sand wasps burrow into the sand to create nest chambers for their larval young. The various species usually specialize in fly species to stock the nests with. What’s unusual about them is they’re “progressive provisioners.” In other words, while other solitary wasps like cicada killers, mud daubers, and digger wasps create multiple chambers, stock the chambers with prey, lay eggs on the prey, ultimately cover and abandon the nests leaving the young to feed on the paralyzed prey within, these sand wasps feed their larvae as they grow, sort of like song birds do, sort of.
I was wrong about this wasp, though. I was able to photograph one of the wasps bringing in prey. It didn’t look like a fly, but I couldn’t determine what it was until I viewed the image on the computer. The telltale flaring tarsi on the hind legs gave it away. It was a leaf-footed bug. These weren’t the wasps I thought they were at all, Bembicina yes, but not Bembix.
It took a little hunting to figure it out, but after watching a few more wasps fly in with stink bugs to store away in their nests, I’ve settled on Bicyrtes quadrifasciatus or four-banded stink bug wasp.
Different from Bembix, Bicyrtes don’t progressively provision the nest, but stock pile it with enough prey to feed the larva for the duration. They then leave an egg inside the chamber, seal it off to the outside world and go off to do it again elsewhere.
I took one of the stink bugs away from its captor to photograph it, hoping to establish an identification. I suspected more than one species and so far all I’ve seen were nymphs, not adult bugs.
Doing further research, this wasp apparently specializes in nymph stink bugs and plant bugs like the leafed-footed bug I first witnessed being brought in for storage (first two photos). Both stink bug nymphs brought afterward were brown marmorated stink bugs (Halyomorpha halys). Marmorated means streaked or marbled.
Curiously, the wasp flew off, didn’t object to me removing its captive and stayed out of view for several minutes. It, or another wasp just like it, eventually came back to the scene, flew over, landed and walked around the immobile stink bug a few times and then began to toss sand into its burrow. While ants proceeded to investigate and dismember the stink bug, the wasp filled its burrow with sand, concealing the entrance.
What was this wasp doing, ignoring a perfectly good stink bug lying on the sand only inches away from its burrow. Perhaps, like a domestic cat chasing a mouse, once the mouse stops moving the cat loses interest. Could it be some instinctual mechanism which is triggered by the mouse’s movement shuts down after that movement ceases, the wasp no longer interested in the stink bug after it was removed from its burrow entrance (the wasp was deep in the burrow when I absconded the stink bug and didn’t actually witness the event).
Whatever process it was that was at work here, the wasp covered its burrow and took flight. Did it intend to capture another stink bug and finish stocking the burrow for its future larva? or had it already done all it was going to do in this burrow and had moved on to another excavation?
I do not know the answer to those questions, I was not able to follow up, having other duties to perform. I do, however, intend to spend more time watching this sand pit for more insect adventures before it opens to visitors and the wasps are asked to move on.
The identification of the stink bugs are thanks to Ken Wolgemuth and BugGuide.net, a great resource for insect related stuff, especially identification matters.