Stump Stabber Wasp
By Les Harrison
Wakulla County Extension Director
Generalizations are an easy way to attempt to predict the character of almost any subject or thing without examining the situation or details. The scenario goes if X is present, then Y will occur.
Alas, life is far too complex for generalizations to be of much use and in many cases the simple rationalization lead to incorrect conclusions and occasionally disastrous results. Wasp are a good example of this conundrum.
The common perception of a wasp is as a chronically cranky flying insect which is seeking every provocation to stinging anyone who comes into its range. Yellow jackets, one native species of wasp, leads many to this erroneous conclusion.
Wakulla County is home to multiple wasp species, many which go unnoticed by the human residents. Possibly because there are no recorded incidents of these species stinging people.
Oak gall wasp are barely visible at 2 millimeters in length, which is about the thickness of a half-dollar coin. The wasp’s petite size notwithstanding it is responsible for individual galls which can be nearly a foot in length.
Wakulla County’s oaks, both deciduous and evergreen, are susceptible to a collection of knotty, hard tumor-like growths on leaves, twigs, and limbs. Laurel and water oaks are especially vulnerable.
The bulbous lumps may be few and scattered or come in heavy concentrations. To the uninitiated these arboreal blisters may appear to be oversized and out-of-place acorns, but are really a fundamental part of this species’ reproductive process.
The life cycle of these wasps is not completely understood since they have not been studied extensively. It has been confirmed the sequence begins when the female wasps emerge from twig galls in late spring to early summer.
These females quickly lay eggs on the underside of leaf veins. Small vein galls appear within a few weeks in early summer with male and female wasps quickly emerging from the vein galls.
Mated females then oviposits eggs in young oak twigs. Twig galls appear in the spring of the following year. Two or more years are required for the immature gall wasps to complete development in the twig galls.
The galls provide shelter, protection, and food for the immature wasps. Inside a gall, the larvae are surrounded by nutrient rich tissues.
As the larvae reach maturity small spines or horns become evident on the gall. An adult wasp emerges from each horn.
Another wasp species which uses forest resources to incubate their next generation is commonly known as the stump stabber.
Megarhyssa macrurus, also known as the giant ichneumon wasp by entomologist, is a large, easy to see species of about two inches in body length. Most notable on the females is the ovipositor which can reach four inches in length and have the appearance of an extended stinger.
This wasp’s ovipositor is a combination of three filaments. The middle filament is the actual ovipositor which is capable of drilling into wood and has a cutting edge on the tip.
Unlike the oak gall wasp, the stump stabber wasp parasitizes other insect larvae in the decaying wood. In a few weeks they will have consumed their host and be ready to emerge in the spring.
Generalizations aside, it is safe to say Wakulla County’s many habitats have a wasp suited to live there. Only occasionally are stings to people a confirmed threat.
To learn more about wasp in Wakulla County, contact your UF/IFAS Wakulla Extension Office at 850-926-3931 or at http://blogs.ifas.ufl.edu/wakullaco.