The Nature Writers of Texas

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Sunday, May 30, 2004

Cicada-Killers and other Parasitic Wasps
Ro Wauer, May 30, 2004, The Victoria Advocate, © 2004

All the recent talk about cicadas reminds me that all cicadas and all other insects have natural prey that keep their numbers in check. And many of the natural predators are parasitic wasps that without them our world would be a very buggy place.

The largest and most obvious of these wasps are the various spider- and cicada-killers. The best known of these is the pepsis wasps, blue-winged creatures with a red body that can reach two inches in length. The largest one, although rare along the Gulf Coast but far more abundant throughout the southwestern deserts, is known as the "tarantula hawk." A slightly smaller species - Pepsis elegans - with orange wings and a blue body, is far more common in the Central Gulf Coastal area.
These two impressive wasps spend a good deal of time on the ground walking about in search of spiders. Once an appropriate spider is found, it will sting its prey, depositing just enough venom to paralyze but not kill it. When the spider is subdued, the wasp will then carry or drag its prey, depending upon the size of the spider, to a hole that it already has excavated in the ground. It will then cram the spider into the hole, lay eggs in the spider's body, and cover over the hole with the excavated debris. The wasp eggs will hatch within a few days, and the larvae will consume the body of the living spider.

The cicada-killer, known to scientists as Sphecius speciosus, which looks all the world like a huge yellow jacket, is also an effective parasitic wasp. This individual, however, finds its prey above ground in trees. Once it discovered an appropriate prey, it will jab its stinger into the insect's nerve center, paralyzing it. When that occurs, the wasp and prey usually fall to the ground. She will then drag the cicada back up the tree to where she can carry her prey in a direct glide to her burrow. The size of the cicada negates any chance of carrying such a load up and over vegetation, but she has the strength to drag it up an unobstructed tree trunk. Unlike the pepsis wasp, which lays numerous eggs in the body of a spider, the cicada-killer deposits a single egg on the body of the paralyzed victim. And since its burrow usually contains several chambers, it takes several cicadas before its chores are complete.

None of these adult wasps actually feed on their prey. Instead they utilize sap or nectar from flowers. The wasp larvae, however, remain underground feeding on their victim for several days until they reach full size and their food is depleted. Then, rather than emerge as adults, they spin a silken cocoon in which the larvae remain and develop until the following season. Finally, in summer of the following year, they emerge from the cocoons and leave the burrow as adult wasps. And the process begins all over again.

1 Comments:

At 8:53 AM, Anonymous Ethel said...

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