Within the insect order Hymenoptera, family Sphecidae, is the Sphex genus with over 130 recognized species and subspecies. One of the larger and more impressive thread-waisted is the Great Golden Digger Wasp or Sphex ichneumoneus. Aptly named, as the term "ichneumoneus" is Greek for tracker, these robust wasps are known for tracking their prey.
Great Goldens are one-half to over an inch in length, though some sightings have reported seeing them as large as two inches. Great Goldens are easily spotted during the summer. Their black head and thorax are covered with short golden hair. Half of the back segment of their abdomen is also black with their front segment and legs a reddish-orange.
Great Goldens have large amber wings that actually make a rustling noise when they fly. This wasp is related to the Giant Cicada Killer Wasp (Sphecius speciosus, which is common in the Galveston-Houston area) although Great Goldens are a little more wasp-like.
Occurring in North America, Mexico, Central America, South America and the Caribbean, Great Goldens are usually seen in parks, gardens, fields and meadows—anywhere that is sunny, has compacted clay and sand, flower nectar for adults to feed on, and crickets, grasshoppers and katydids for their larvae.
The adult wasps subside strictly on sap fluids and a variety of flower nectars that bloom during their flying time. Spotting them is one thing, but observing them can be dicey. Great Goldens do not linger around a bloom for very long and are quite wary of anything larger than they are. Fortunately, though they may look scary, these wasps are not aggressive unless handled and should be left alone. Great Goldens are solitary wasps, live independently and do not share in either nest maintenance or in the caring of their young.
Between May and August, the female Great Golden, in preparation for egg laying, constructs as many as half a dozen nests. The building of, and provisions for, the nests is done in a concise, methodical manner, which she never deviates from.
Rarely is there vegetation around the nests. Most sites are exposed to the sun in an open locale. The female begins digging, almost vertically, by cutting the earth with her mandibles. She walks about an inch backwards from the nesting site with a section of soil between her forelegs and head and flips the soil with her forelegs beneath her body, scattering it to the sides with her hindlegs.
Great Golden nests have a cylinder shaped main tunnel that is one-half inch in diameter and four to six inches deep. From the main tunnel, she extends secondary tunnels that lead to individual larval cells where she will store anesthetized prey. The cells are broader than the tunnels and parallel to the soil. Once completed, she temporarily closes it after excavation by using the earth that remains by the nest entrance. The female throws it towards the entry with movements identical to those she made when she dug the nest.
After constructing the burrow, she flies from the nesting area to open fields and hunts for any number of small locally available species of Orthoptera. Great Goldens hunt for crickets (Gryllidae), grasshoppers (Trimerotropis) and katydids (Tettigoniidae) to serve as a food source for her young. [Katydid is a general name given to several species of American large green long-horned grasshoppers. Male katydids have stridulating organs on the forewings that produce a loud shrill sound. The eggs are rather distinctive and are oftentimes deposited along leaf margins in rows usually in large trees but also on shrubs. Even katydid eggs can be heavily parasitized by a small wasp, Anastatus mirabilis, which makes a small round exit hole when the adult wasp emerges from the katydid egg.]
Upon capturing a suitable prey, the female Great Golden will paralyze it with toxins in her sting. If the prey is small, she flies it directly to the nest. If prey is too large to transport aerially, the wasp will walk with it across the ground. The prey is clasped beneath her body by grasping its antennas with her mandibles.
Once the Great Golden reaches the opening of her nest, she sets the paralyzed insect down. Leaving the prey outside, she goes into the tunnel for inspection. When satisfied that all is well, she comes partially out from the nest and again grasps the prey’s antennas pulling it backwards into the nest’s interior where it is deposited in a cell with its head turned to the bottom.
Though the prey is permanently paralyzed, it is able to eliminate feces and slightly move its antennas and mouthparts. Great Golden females close the nest each time prey is placed inside. When she re-enters for egg laying, she emits a set of buzzing sounds as she compacts the earth closing the entrance.
There are several behavioral aspects to this “self-programmed” wasp that continue to fascinate as humans tend to think such rote habits denote forethought and logic. Douglas Hofstadter and Daniel Dennett, two professors of Cognitive Science, 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, with the Sphex never seeming to notice what is going on, never able to escape from its genetically programmed sequence of behaviors. The wasp never "thinks" of pulling the prey straight in, but continually drops it outside until she is done with her nest inspection.
Using this as an example of what may seem as thoughtful behavior can actually be quite mindless, the opposite of what is considered free will (or, as Hofstadter described it, “antisphexishness”). 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.
After the Great Golden has dragged all her paralyzed prey into the nest hole, she lays one egg on each insect, placing it horizontally on the prey’s thorax. The eggs are yellow, less than a ¼ inch long and has a slightly curved cylindrical shape. They hatch within 2-to-3 days of oviposition, and without moving, they begin to feed on the prey’s abdomen or at the junction of its leg. The feeding phase is very rapid. In one of the observed cases, the larva consumed even the more rigid parts of the prey’s exoskeleton.
There is one generation per year with the developing Great Goldens spending the winter in their nests and emerging in summer. Once this new generation of adults comes out, they contain the inbred behavior that is only seen in this species.
As a side note there is a reference to birds stealing prey from Great Goldens. House sparrows (Passer domesticus) and American robins (Turdus migratorius) were observed stealing from them at a large nesting site. The birds chased wasps that were carrying prey to their nests, causing them to drop the food, which the birds then retrieved and ate.
In another instance, a male Scarlet tanager (Piranga olivacea) flew directly at a flying wasp causing her to drop an insect, but this time the bird did not pick it up. After being robbed of its prey, the wasp either left or flew in tight circles around the back of the bird until it flew away, or if the bird was on the ground, dove back and forth around its head. The wasp’s behavior never scared the bird. Large concentrations of Great Golden females are quite vulnerable to attacks by birds as the prey the wasps bring in are an easy food source for the birds. There is no record of any other species of digger wasps known to be harassed by birds in such a fashion.
Unfortunately, homeowners, who have these foraging wasps around their landscape and dig holes in their lawn, usually reach for a can of insecticide. Great Goldens are benign, do not defend their nests, are not aggressive and definitely do more good than harm. Hold that can for a moment and realize that like many other wasps, the Great Golden Digger Wasp is quite beneficial to both gardeners and farmers. So please leave them alone to do their job.
Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.
All digital photographs are the property of the Galveston County Master Gardener Association, Inc. (GCMGA) 2002-2015 GCMGA - All Rights Reserved.