Digger Wasp beside prey

Female Great Golden Digger Wasp beside her paralyzed Katydid prey. A still grab from 4 K video, shot on LUMIX DC FZ80, C. Paxton image and copyright.

Kimmie scouts some of the best wildlife encounters for us. One such was with this very plucky female Great Golden Digger Wasp (Sphex ichneumoneus) pictured above. A very characterful, busy little creature, just over an inch long, with purplish glossy, transparent wings folded neatly over an orange-brown abdomen with black tip. Her golden head and neck fuzz, collar and shoulder trimmings and her energetic earth workings give her her English name, these along with her large shiny compound eyes won our affection instantly. She was so sweet! More of that later.

Kimmie had noticed that a burrow had appeared in the front lawn of her grandparents’ home under the shade of a large Popcorn (Chinese Tallow) tree. The following day, before breakfast, she saw the wasp responsible, hard at work, digging out this nest burrow and called me over quickly. The Sphex was so sweet and perky. Her moves so crisp and deliberate! She scooted up and down a little sandy run and then disappeared neatly down her burrow, only to emerge again backwards after a short while with a clump of sand between her curved orange fore-legs. This sand was then flung very quickly underneath her between her legs and then back she’d go for more. On  occasion she would spend a little extra time above ground splaying out her legs to spread the sand. This gives the rather amusing appearance of her ‘revving up’ to go back down her hole. At first I didn’t even see the sand being spread, I just saw her revving up and down her little track, constantly feeling the ground ahead of her alternately with each feathery antenna and occasionally flapping her wings a little!

We immediately returned with the Lumix cameras and set to filming her endeavours in UHD at 30 FPS and in high speed HD (130 fps) mounted on a tripod and lain on a rice bag. She was very tolerant of our presence and so preoccupied with the task of excavating her nest burrow that we were entirely free to get down low and get in close! The tiny quartz crystals looked a little like precious stones when enlarged in close-up. She looks great in the 4K video and her moves are so fast that they were blurring at 30 fps.  She even allowed the tripod to be set directly over her hole! They are non-aggressive. Don’t try such liberties with the eusocial wasps (like Red Wasps) as they are not as sweet-natured as the solitary wasps and unlike this tolerant Sphex, they have learned to respond to stranger danger in close proximity to their nests highly defensively and rank a high 3 out of 4 on the Shmidt Pain index. You may have heard people yelling “Oh Shmidt!” or words to that affect when being stung by social wasps?

The entomologist (insect scientist) developed his sting pain scale as part of his broader study into the dependence of the development of wasp society upon development of venom that was both painful and toxic. Pain without damage was insufficient to dissuade hive/communal nest predators like people, bears and honey badgers. Gathering together in hives makes it easy and worthwhile for predators to attack their grubs (pupae) all at once, so it was necessary that the eusocial wasps developed such very strong, dissuasive stings. The strongest wasp venom actually belongs to the solitary ‘Mule Killer’ Tarantula Wasps, but lets face it, when you’re up against big spiders with large fangs you need to be that well-armed! With grasshoppers? Not so much.

Sphex ichneumoneus carrying between its forelegs

Sphex ichneumoneus carrying excavated sand between its forelegs. A task I equated with picking up sand with chopsticks! K. Paxton image and copyright. Lumix GX8 with 14-45mm lens and 16mm extension ring.

Later that morning we returned and filmed our Sphex some more. After reviewing our footage I returned to reshoot some top-down sequences in manual focus because the autofocus hadn’t worked too well then, and I was disappointed to find no burrow!

Furthermore it wasn’t very clear where the burrow had been. If we hadn’t the photographic evidence to prove where she’d been digging then we might have doubted our memories. By this time we had got an ID for her on iNaturalist and knew something of her lifestyle, that she was a solitary parasitoid wasp that preys upon katydids, bush crickets and horned grasshoppers, so a farmer/gardener’s friend, not a pest species. I was pleased to have seen her but choked to have missed her burying her prey.

I’ve always thought wasps to be pretty cool creatures but our research into them further increased our interest in them. Their Order, the Hymenoptera, includes Sawflies, Bees and Ants and their common ancestor dates back to the Jurassic period. The smallest flying insect on Earth is a kind of wasp!  There are hundreds of thousands of wasp species (The UK alone has about 6000!) and most of them are solitary and many are highly attractive and jewel-like, they have some of the most specialized lifestyles known to science and a great many other species depend upon them for survival.  

We learned from several sources that the female Sphex meets her mate elsewhere and then raises her family alone in side chambers off a tunnel that she excavates in sandy soil as a brood nest.

Kimmie shooting UHD footage of the inch-long Sphex as she scoots in and out of her nest burrow. C. Paxton image and copyright.

She favours sandy soils above clay for her burrows and that fields and gardens provide good habitat for hunting her prey. First she digs a tunnel that can be up to six inches deep and have multiple brood chambers leading off from the main tunnel. Then she hunts for an insect which she stings with a paralytic venom, then returns with it to her nest and pulls it down into her tunnel and then stuffs into one of the brood chambers and lays an egg on it. She will then rebury her tunnel to conceal it from brood parasites. This is just as well because we actually saw a brood parasite wasp from the Tribe Nissoni buzzing about her tunnel while she was absent and go down into the tunnel, presumably to lay her own eggs. This was before we saw her return with her prey.

A brood parasite in Tribe Nissoni, perhaps N. aequalis, sneaking in to lay her own eggs.

Sphex ichneumoneus can bury up to seven insects within one brood burrow and she makes more than one burrow in a season. They are subject to attack from several cleptoparasites, including other wasps and some birds will harass them for their food. (For more see insectidentification.org)

According to the excellent Galvaston Master Gardeners’ website she’ll build up to 6 nests from May to August. Each tunnel is 1/2 inch across and from 4 to 6 inches deep with branches that lead to individual cells. She’ll close off her nest temporarily while she hunts and retrieves her prey. She carefully inspects her tunnel just before she puts the prey in, this has been identified as “‘self-programmed’ rote habits that resemble “forethought and logic”.” Two professors of Cognitive Science, Douglas Hofstadter and Daniel Dennett, ” created a controlled environment to study the Sphex routines more closely. After the Great Golden dropped her prey and was inspecting her nest’s interior, the professors moved the prey a few inches away from the opening. When the wasp emerged ready to drag the prey in, she found it missing. Quickly locating the prey, the professors believe her ‘behavioral program had been reset’ as they found that, once again, she dragged the prey back to the threshold of the nest, dropped it and repeated the nest inspection procedure. During one study, this was done 40 times, always with the same result. This test can be replicated again and again… The wasp never “thinks” of pulling the prey straight in, but continually drops it outside until she is done with her nest inspection…  In addition to this apparent inborn, programmed behavior, Sphex has been shown, in some studies, not to count how many insects it collects for its nest. Although she may instinctively search for a certain number of insects, she is not an able take into account one that is lost.”

For more on this see https://aggie-horticulture.tamu.edu/galveston/beneficials/beneficial-54_great_golden_digger_wasp.htm

Or if you open a free COVID-19 enabled account you can view the original paper on JSTOR

clicktoviewWatch the movie Wasp Watching: The Great Golden Digger Wasp (Sphex ichneumoneus) on Wildopeneye Channel on YouTube.