The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, August 13, 2006

Parasitic Wasps Are Widespread
by Ro Wauer


Nature is full of checks and balances, from multitudes of tiny hard to see creatures to much larger ones such as wolves and tigers. I doubt, however, if Jonathan Swift, author of Gulliver' Travels, had that in mind when he wrote that "Little fish have bigger fish that feed on them and bite ‘em, and big fish have still bigger fish, and so, as infinitum." But it fits perfectly! Swift probably was thinking of fishing, and not about nature’s pyramid of life. And yet we have recently experienced several examples of the relationships between parasitic wasps and other organisms. Think about the enormous flight of snout butterflies, a major explosion in numbers partly because of a significant decline of their parasitic wasps that normally would help keep their numbers in check.

Another recent event provided one more example of a parasitic wasp that is instrumental in controlling another group of insects that has been singing loudly in our neighborhoods. This is the cicada-killer wasp, a fairly large, heavy-bodied wasp with a black abdomen with yellow rings, black thorax, and clear wings tinged with rusty color. It, too, is a deadly predator. Female cicada-killers dig burrows, usually about a foot in depth, and search out cicadas that they paralyze with a sting. Most cicada-killers find their prey above ground in trees. Once it discovers 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. It is much easier, apparently, to drag her prey up the tree and then glide it to its burrow. She will then deposit a single egg on the body of the paralyzed victim. The resultant larvae will then gradually consume its host. And since its burrow usually contains several chambers, it takes several cicadas before its chores are complete.

And anyone who has spent much time in the field, especially in the Southwest, cannot help but notice the large, blue-bodied, reddish-winged wasps known as tarantula hawks. Like cicada-killers, this large wasp seeks out tarantulas to subdue with a sting that paralyzes the spider but keeps it alive. These impressive wasps spend a good deal of their 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 several eggs in the spider's body, and cover 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.

Such stories occur throughout nature, involving a wide assortment of creatures. A few additional examples involving wasps include the ichneumon wasp that utilizes the eggs of another wasp, wasps and bees, wasps and beetles, wasps and earwigs, wasps and fleas, wasps and flies, wasps and lice, wasps and ticks, wasps and aphids, wasps and huge variety of caterpillars, and on and on.

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 emerging 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 as adult wasps. And the process begins all over again.

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