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Earlier this summer, an eight-inch pile of dirt adjacent to a 1/2" tunnel appeared under the bay tree in my herb bed. As the weekend progressed, I checked it as I went in and out my back door, never catching a glimpse of the burrower.
My grandson Brennon was visiting on Sunday afternoon and we were doing the usual circuit through the back yard looking for spiders, anoles, earthworms and caterpillars. I thought a hummingbird zoomed toward the bay tree, but we were busy and I didn't stop to investigate.
Later, Brennon wanted to find out what animal lived in the tunnel so we crouched down and were taking turns peering down the hole, speculating on what might be inside. Suddenly, a huge wasp barreled out of the tunnel, leaving us scrambling backward to get out of its way.
What I thought was a hummingbird turned out to be the largest wasp in North America - a Cicada Killer carrying a paralyzed cicada to its nest. A little Internet research gave me quite a bit of information about these gentle giants.
Identification, Disposition & Range
The adult Cicada Killer is a very large (1-1/8 to 2" long), robust wasp with a black body marked with yellow across the thorax and on the first three abdominal segments. The head and thorax are rusty red, wings are brownish, and legs are yellowish. Coloration may resemble yellow jackets or hornets. The females are considerably larger than the males, enabling them to carry cicadas to their nests.
In spite of their large size, these wasps usually ignore people. Female Cicada Killers rarely sting unless disturbed; however her sting causes pain that may last as long as a week. Mating males have especially aggressive territorial behavior, but have no sting - they'll inflict a painful bite instead.
The main difference between bees and wasps is that bees feed their larvae a mixture of pollen and nectar (honey), whereas most wasps feed their larvae meat, mainly paralyzed arthropods. Like bees, adult wasps feed on flower nectar and sap exudates.
There are many species of solitary wasps. In fact there are far more species of solitary wasps (Cicada Killers, mud daubers and potter wasps) than there are social wasps (hornets, yellow jackets and paper wasps). Solitary wasps are very different from social wasps in that females use their sting to paralyze their prey rather than to defend their nests.
Cicada Killers live in all states east of the Rocky Mountains in areas where annual cicadas are prevalent.
Mating & Nest Building
Males emerge from the burrows first and then stake out territories where females are likely to emerge. The males defend the airspace within their territories against other males, and chase anything that flies on the chance that it might be a virgin female.
Soon after the females emerge, they mate just once. The male occupying the territory in which the female emerges is usually successful in mating her. After they fall to the ground, the male climbs atop the female, grasps her head in his mandibles and proceeds to shake her head from side to side. After this bit of wasp foreplay, copulation takes place. Other males may try to horn in, forming a cluster around the mating pair. Males in this cluster have been observed grasping and shaking other males' heads before they lose interest and leave in search of an eligible female.
After mating, the female selects a nesting site. Each female digs her own burrow and may tunnel as much as six inches deep and another six inches horizontally. At the end of the burrow are usually three to four cells where one to two cicadas and one egg are placed in each cell. If all the cells are filled, secondary tunnels are constructed and provisioned. A single burrow may eventually have 10 to 20 cells. Nests usually are made in full sun where vegetation is sparse, especially in well-drained soils - but sometimes in planters, flower beds, under shrubs and ground cover. Once cells have been constructed, the search for cicadas begins.
Females search tree trunks and lower limbs for cicadas, apparently by vision rather than sound, suggested because the majority of their prey are female cicadas which make no sound. Cicadas are paralyzed by the venom of the wasp's sting, and will remain alive during the feeding of the wasp larvae. The prey can weigh up to three times as much as the predator, so most wasps drag cicadas along the ground and up a tree or other vertical object, from which they can launch themselves downwards toward their burrows. Without the presence of trees or shrubs, she will walk on the ground.
Females hunt and lay eggs continuously when conditions are good (warm, sunny days with low humidity and lots of cicadas singing) and use of their burrow falls into a typical pattern. A female will leave the burrow after digging a cell, hunt for a cicada, return to the burrow with it, stay in the burrow for three minutes or so, and leave to hunt again. Or she will stay in the burrow for 45 minutes while she lays an egg on a cicada and closes the cell with dirt made by digging a new cell, after which she will leave to hunt again. A female will return to her nest from an unsuccessful hunt, inspect it, then leave to hunt again.
Each cell is furnished with at least one cicada (sometimes two or three) and a single egg before being sealed. An egg laid in a cell with one cicada produces a male larva, and an egg laid in a cell with two or three cicadas produces a female larva. Two to three days later the egg hatches. Depending on the number of cicadas in its cell, the larva feeds for 4 to 10 days until only the cicada's exoskeleton remains. During the fall, the larvae spin a cocoon and remain in the cell through the winter, emerging as adults the following summer. Only one generation occurs each year.
Once she seals the last cell, the female's role is finished. Her average life span is only two weeks.
Read more about these and other beneficial wasps at these websites:
Prof. Chuck Holliday's Cicada-Killer Page
The Cicada Killer Thriller Page
Scott's Bee and Wasp House