Monday, July 19, 2010

Wasps: Friend or Foe?

A few years ago I had a thriving crop of broccoli in my garden. Then the leaves started getting holes. The holes got bigger. I looked for the culprit and found little green caterpillars, probably cabbage loopers. I picked off as many as I could find. I continued to do so for 2 or 3 weeks and didn’t really seem to make any headway. They reproduced faster than I could remove them and removed foliage as fast as it grew. Then one day I noticed that I had finally gotten ahead of the caterpillars. The damage seemed to be abating and I couldn’t find a single one. As I looked over my plants, trying to find any of the little green caterpillars I may have missed, I noticed I was not the only one. A wasp came to the plant and flew over each leaf in what was obviously a search pattern. It occurred to me right then that I probably had nothing to do with the lack of pests while the wasp had everything to do with it.

Wasps are voracious predators of a wide variety of garden pests. While the adults eat a varied diet, consisting mostly of pollen, nectar, and insects, the young are a bit more specialized. They eat insects. Many wasp larvae are actually parasitic, meaning that they live inside the bodies of larger insects, eventually killing them when the wasp matures. This means the adult wasps, many of which are good parents, go out and find large insects to feed to their young, often choosing ones that damage our gardens. An active wasp nest can seriously deplete your pest population in a hurry.

So what is a gardener to do? Well, first of all, if you are allergic to wasp stings, I strongly recommend not taking the chance. I am not allergic, so I let them be, mostly. Most wasps spend a little time on the plants, do their stuff, and then move on. I let those be. I do swat the ones that take a special interest in me, my children, or my food, though.

Let me leave you with one last wasp story. When I was about 15 years old, I got my first pitcher plant, a carnivore that needed a steady supply of insects. It was small, with only 3 or 4 traps and only an inch and a half tall or so. So I put the whole terrarium outside for the summer. I wanted to attract insects, so I put a little piece of peach in the terrarium with it, thinking it would attract fruit flies. I got a few fruit flies, but the fruit was dominated by wasps, which mostly scared the fruit flies away. I was pretty upset about it, but didn’t know what to do. I thought about it for a few days and then looked again. One of my tiny traps had a wasp abdomen sticking out of it. I was sure the wasp would rot and kill the trap, but it didn’t. I soon stopped providing fruit and the pitcher plant did just fine attracting the wasps itself, catching 2 or 3 a week all summer. By the end of the summer my pitcher plant was 3 or 4 inches tall and had 15 to 20 traps on it.

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