Insect Horror Movie!

The plot and the characters are in place for a terrific new insect horror film. The ads would read like this…“Giant caterpillerzilla threatens food supply until air force saves the day with new deadly smart bombs…and it’s all going on in your backyard.”

Actually it is not a movie, and it is nothing special, it is just an everyday happening in nature. The following is a true story.

If you have ever grown tomatoes you are probably aware of those giant green caterpillars called Tomato Hornworms. These things are as big as your thumb and they look like they could swallow a finger, but their green camouflage color make them extremely difficult to see on a tomato plant. There are three ways to spot them. First, if your tomatoes are in a container on a deck (like mine) you might see the little black droppings of the caterpillar on the deck. That is your clue that a Tomato Hornworm is in the vicinity. Another way to find them is to notice that the leaves are missing from a whole stem on your tomato plant. In these two cases you can then step back and carefully search the plant for the Hornworm. The third way to find a Tomato Hornworm is the scary way. You are reaching for a tomato and you notice a very, very large, green, caterpillar with a dangerous looking spine on its backside about an inch from your fingers. When you spot them this way it is sure to jolt you to attention in a hurry.

The Tomato Hornworm is the caterpillar form of a moth called a Hawk Moth. The moth lays its eggs on tomato plants and the larva (caterpillar) eats leaves voraciously and grows quickly to 3 or 4 inches long and ½ inch or more thick. A couple of them will strip a tomato plant of all its leaves if you don’t remove them. I usually remove them with a pair of pliers and if you have had them you know that they don’t let go easily.

So that is the first part of the story of the big scary caterpillar and the threat to your tomatoes. But the rest of the story is the interesting part and the gory part of this nature documentary.

There is a tiny ½ inch wasp called a Brachnid Wasp that we probably never notice, that preys on the Tomato Hornworms. Their smart bomb method is devious and deadly. The wasp locates a Hornworm and injects it under the skin with numerous eggs. The eggs hatch in a couple of days into little wasp larva like tiny maggots. The larva feed on the caterpillar from the inside. They don’t kill the caterpillar yet, they just cause it to stop feeding. However, I am sure that the caterpillar is not feeling too frisky at this point. In a few days the larva bore out and form cocoons on the outside of the caterpillar. The picture in this article shows a Tomato Hornworm caterpillar covered with these tiny cocoons. In a few more days the young wasps hatch and go on their way looking for more Tomato Hornworms to prey on. The air force to the rescue! The host caterpillar dies without causing any more damage to your tomatoes.

It is estimated that by late summer that 90% of all Tomato Hornworms are parasitized by the tiny Brachnid Wasps. This is natural insect control by another insect. This is not a unique case; there are a number of types of wasps that parasitize other insects or spiders in this way.

So let nature help. If you see one of those scary Tomato Hornworms covered with tiny football shaped white cocoons let it be. The Hornworm won’t be feeding any more and if you let the wasps hatch there will be that many more of your tiny wasp buddies helping to control a common garden pest.

Nature can be scary, exciting, interesting, fun, and kind of gory at times…and it is happening in your backyard.