Female and male five-banded thynnid wasps look quite different. Both sexes are banded with black and yellow, but the females are large and heavy-looking, while the males, often seen in groups, are much skinnier and possess a scythe-shaped false stinger on the hind end.
Females are usually described as “robust”; the legs are rust-colored, and the femurs (thigh-like segments) of the hind legs are thick and heavy-looking (these wasps dig into soil); the main body of the antenna is orangish or rusty, and the base has some yellow on it.
Males have thin bodies and longer, thick-looking, straight black antennae. A black, curved, pointy pseudostinger is at the abdomen tip; this is not a real stinger (males are incapable of stinging). Often seen clinging to a plant in a group.
Similar species: There are 10 species in the genus in North America north of Mexico, but the five-banded thynnid wasp is the most common species in the eastern United States. Note the characters described above, and seek out the many images online to get a precise ID. Other species in the genus that occur in Missouri include M. carolinianum, M. maculatum, and M. obscurum. There are more than 60 species worldwide, all in the New World. This and related groups of wasps have presented headaches for taxonomists because the males and females can be so different, requiring two painstaking sets of ID characters per species. For perfect IDs, specialists use detailed descriptions of the shapes of reproductive organs.
Length (not counting appendages): approximately ¾ to 1 inch.
Statewide.
Habitat and Conservation
Most people see this species visiting flowers in open areas such as prairies, old fields, roadsides, and sunny gardens. They are usually seen in late summer or early fall. In Missouri, July, August, and September are the prime months.
The robust females are usually seen singly, while the comparatively slender males are often seen congregating on a single plant. Their aggregations are thought to help the males survive potential predation. See Ecosystem Connections below.
Food
Most growth occurs in the larval stage underground, as the immature wasp consumes the body of its host, which is some kind of larval scarab beetle. Examples include the C-shaped whitish grubs of Japanese beetles and of May beetles (also called June bugs). Because the latter are native and numerous (with a variety of species in the eastern United States), they are probably the native host for these parasitoid wasps. The boom in recent decades of the invasive Japanese beetle has no doubt meant a boom for these wasps, too.
The larval wasps are called parasitoids because they do not immediately devour their hosts. They begin as parasites, eating only nonessential portions of the host, but when they grow larger and are nearing the time to pupate, they consume the rest of the host.
Comparatively less time is spent in the adult stage, and adults drink nectar from flowers to sustain themselves through the tasks of reproduction. Adult five-banded thynnid wasps are especially fond of flowers in the aster/sunflower family (Asteraceae), carrot/parsley family (Apiaceae), mint family (Lamiaceae), and dogbane/milkweed family (Apocynaceae). Look for them taking nectar on native yarrow, goldenrods, thoroughworts (bonesets), sunflowers, rosinweeds, crownbeards, wild quinine (American feverfew), rattlesnake master, mountain mints, wild bergamots, and various milkweeds and dogbanes.
Status
Thynnid wasps are usually labeled “beneficial” to human interests because they prey on, and help control the populations of scarab beetles that are considered agricultural or landscaping pests. These and other scarab-hunting wasps are often considered effective biocontrol agents.
Only the females can sting, but they reserve their stings for their prey. They only sting people if they are mishandled, stepped on with bare feet, or otherwise feel their lives are endangered.
Taxonomy: the thynnid wasp family (Thynnidae), to which this species belongs, used to be considered a subfamily of the tiphiid wasp family (Tiphiidae). Both groups are sometimes called “flower wasps,” though there are many, many other wasp families that also visit flowers. In both families, the females hunt and lay eggs on underground beetle larvae (usually the grubs of scarab beetles).
Life Cycle
Females dig into soil and make their way to the larva of a scarab beetle. Resting on the soil surface, apparently they use their sense of smell and/or can feel vibrations of the grub moving around underground. Finding a grub, she paralyzes it with a sting and lays a single egg on it. The wasp larva hatches and enters the host’s body. At first, it consumes tissues and organs that are not critical for the grub’s life, but eventually it eats the vital organs and kills the grub. Its feeding completed, the larva becomes a pupa and overwinters in this stage. The adults emerge in summer, mate, and continue the cycle. There is only one generation each year, and the timing of emergence coincides with the availability and abundance of beetle grubs and their positioning in the soil.
Human Connections
This and other thynnid wasps are beneficial to human interests because they prey on larval scarab beetles, helping to control their populations. Many scarab beetles are considered pests, including the invasive Japanese beetle, which defoliates a wide range of plants, and the various species of May beetles/June bugs, whose root-eating larvae can cause browning in turf grass. These wasps are often considered effective biocontrol agents, as they destroy larval beetles before they can reproduce.
These wasps may seem formidable, but they are virtually harmless, unless you mishandle a female. Only the females can sting, but they reserve their stings for their prey and are not aggressive. Being solitary wasps, they have no colony or “hive” of sisters to defend. The skinny males, often seen in clusters on a single plant, possess a scary-looking scythe-like appendage on their hind ends, but these are not stingers and cannot harm people.
As with nearly all wasps, bees, and other insects possessing venom, some persons may be especially allergic and may have a bad reaction to being stung. If you’ve been stung and have difficulty breathing, seek help immediately.
Ecosystem Connections
These wasps play a role in pollination. As predators, they help control the populations of the insects they eat. As prey, they are consumed by a wide range of predators: assassin bugs, robber flies, mantids, spiders, kingbirds and other flycatchers, plus plenty of other insectivorous animals. Animals that dig in the soil help aerate it and allow rainwater to penetrate into the ground.
The roosting aggregations of males in this genus are interesting, and there are several other kinds of wasps and bees whose males do the same thing. The five-banded thynnid wasp is a good example. Males spend the night, or the hottest part of the afternoon, clinging together to a single section of plant stem and nearby leaves. The same individuals typically reuse the same plant over and over; it’s sort of like a napping club. The males in these sleeping aggregations often become so sluggish they cannot mount much of a defense if attacked. Remember that males are incapable of stinging. Apparently, this aggregating behavior dilutes the risk, for any individual male, of being the unlucky victim in case a predator such as an assassin bug discovers the group. In a group of 100 wasps, a single individual has a 1 percent chance of being devoured if discovered. In a group of 25 wasps, he has a 4 percent chance. But if he’s only one of a pair of wasps, his risk goes up to 50 percent.
Thynnid wasps are parasitoids of larval scarab beetles, but they can also be parasitized by velvet ants and bee flies, which deposit their eggs or larvae on the eggs or juvenile thynnid wasps and consume them.
Yes, only female bees and wasps can sting. The stinger in these groups evolved from an organ called the ovipositor (a tubelike egg-laying organ), which only female insects possess. You’ve probably seen the non-stinging ovipositors projecting like needles or tiny, flat swords from the hind ends of female crickets and katydids. These are inserted into the soil or into plants, and the eggs are injected where they need to go. In the case of almost all stinging bees and wasps, the ovipositor-stinger, now that it's equipped with venom glands, can no longer function as an egg-laying tube.
Most male wasps rely on their resemblance to stinging females for protection from predators. But the pointy, curved pseudostinger on the hind ends of males, though it has no venom to deliver, can still function as a weapon in self-defense. It’s better than nothing: A jab with a pseudostinger, especially if an enemy might be expecting a bona fide sting, might be the difference between survival and “gulp.” The males of several groups of wasps possess some form of pseudostinger(s).
