The eastern stizus is a large, solitary wasp that is often misidentified as the better-known eastern cicada-killer wasp (Sphecius speciosus). Like the cicada killer, a single female eastern stizus wasp digs a tunnel into the soil, where she will lay eggs and store provisions for her offspring. Unlike the cicada killer, which hunts cicadas as food for her larvae, the eastern stizus provides her offspring with katydids.
Similar species: Missouri has a number of large wasps that can be confusing until you look carefully at their markings.
- The most common similar Missouri wasp is the eastern cicada-killer wasp (Sphecius speciosus). It looks almost exactly like an eastern stizus. But look closely at the yellow markings: in the eastern stizus, the yellow abdominal marks are smooth-edged, while on the cicada-killer, ornate black hook-shaped edges intrude into the yellow. Also, the color patterns on two of the thorax segments are different: in the eastern stizus, the scutellum and postscutellum plates (compare pictures of the thorax, and you'll see which plates these are) have a distinct pattern of yellow marks, while those plates on the cicada-killer have a plainer, rust-colored patch.
- The European wasp or giant hornet (Vespa crabro), introduced from Europe, is also present in Missouri. Its large, springtime queens can be nearly 1½ inches long and its workers about ¾ inch long. They are social wasps that build big round, papery nests something like those of bald-faced hornets; the nests of European hornets are typically built in dark hollow locations such as hollow tree trunks, but not underground. Being a large wasp, the European wasp is sometimes confused with the much-hyped, introduced northern giant hornet (a.k.a. Asian giant hornet or "murder wasp," Vespa mandarinia), which is not present in Missouri: in North America, that species has been found only in the Pacific Northwest.
Adult length: about 1¼ inches. (Slightly smaller than the maximum size of eastern cicada-killer wasps.)
Habitat and Conservation
The eastern stizus, like the eastern cicada-killer wasp, belongs to a group of solitary wasps called sand wasps (subfamily Bembicinae) within the crabronid family (the Crabronidae, sometimes called the square-headed wasps). Like other sand wasps, the eastern stizus prefers to dig its tunnels into sandy or other loose, easily-worked soil. This is why they are often seen in yards, gardens, stream edges, and golf courses.
Adult eastern stizus wasps are often seen in open areas as they feed on nectar on flowers.
After hatching from its egg, the young, grublike eastern stizus larva eats the body of the katydid its mother provided for it. The katydid(s) provided for the larva are enough for it to grow through all the larval stages and to pupate.
As adults, eastern stizus wasps sustain themselves by drinking nectar from flowers. Most people seem to spot eastern stizus wasps while they are visiting flowers.
Like other solitary wasps, the eastern stizus is not aggressive. Females are capable of stinging, but they reserve their stings for the katydids they hunt — not for fiercely defending the nest. They only sting people when mishandled, constrained, stepped upon, or otherwise provoked. They do not go after people.
Males are incapable of stinging. In the height of mating season, males commonly patrol areas where females are likely to appear, and when males are buzzing around looking for females (or chasing off rival males), they can seem intimidating.
People usually see adults in mid to late summer, often when the wasps are visiting flowers. It is also common to see the males patrolling for mates and the females digging nest holes, hunting katydids, and dragging katydids into the tunnels.
Inside the nest tunnel, the female lays an egg on or near the katydid(s), then closes the tunnel. The egg hatches, and the grublike larva eats the katydid. After molting a few times, the larva pupates and overwinters. In summer, it will emerge from pupation as an adult, claw its way to the surface, and repeat the cycle.
The eastern stizus is one of many wasps that almost never sting humans. Although they are capable of stinging if mishandled or stepped on with bare feet, they are not social like bees and yellow jackets and are never fiercely defensive the way those communal insects can be.
Plenty of people — people who are proud of their ability to identify insects — have misidentified the eastern stizus as the look-alike cicada-killer. Pat yourself on the back when you have learned to tell the difference!
The eastern stizus isn’t the only big, solitary wasp to hunt katydids and use them to provision their larval nurseries in underground tunnels. The great black wasp (Sphex pensylvanicus) and great golden digger wasp (Sphex ichneumoneus) are two more Missouri wasps you might see flying around with paralyzed katydids. All serve as a check on katydid populations.
Although they prey on katydids, eastern stizus wasps are themselves preyed upon by a group of wasps called velvet ants. The female velvet ant sneaks into the wasp’s tunnel and lays an egg in a nest cell. The wasp larva hatches, eats its katydid, and grows; when it pupates, the velvet ant larva eats the pupa.