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One of the greatest parasitoids, responsible for many moth and butterfly deaths, is the braconid wasp.
This sight is one that most people recognize.
What most of us don’t realize is that these are not eggs. These are cocoons. We never see the eggs that begin this process.
Braconid wasps lay eggs in or on the caterpillar.
The eggs hatch and the young wasp larvae drink the blood/hemolymph as well as non-essential organs of the caterpillar while the caterpillar is still eating and growing.
As the caterpillar grows, so do the wasp larvae. The wasp larvae do not take as long to mature as the moth/butterfly caterpillar.
Before the caterpillar is ready to pupate, braconid wasp larvae will leave the caterpillar by eating holes in the caterpillar’s skin/cuticle. They work their way out of the body, to the outside of the caterpillar. At that point, the larvae immediately begin making their cocoons.
There are two basic types of braconid wasps that parasitize butterfly and moth caterpillars.
1) One type attaches its cocoons on the caterpillar itself.
2) The second creates ‘zombie caterpillars‘, having made a chemical change in the brain of the caterpillar, causing it to live the rest of its life protecting the wasp cocoons.
Depending upon which type of braconid wasp is emerging, the cocoons are made either on the caterpillar or by the caterpillar.
1) The braconid wasps that attach themselves, stay on the caterpillar. The make their cocoons attached to the caterpillar, at the holes where they emerged. The caterpillar continues to live for a few days, sometimes moving about a little, but not eating and growing. It is now dying.
2) The braconid wasps that cause caterpillars to protect the wasp’s cocoons will make their cocoons either jumbled and/or under the caterpillar. Some make a stack of cocoons, one on top of the other.
Some of these wasps have made chemical changes in the brains of the caterpillar that causes the caterpillar to cover the stack with its own silk after the wasp larvae have made their cocoons. The caterpillar then sits on top of the stack of cocoons and protects them, the best that they can, from anything that approaches the stack of cocoons. They strike at intruders with their heads or abdomens. The caterpillar never eats again. It continues to protect the wasp cocoons until it dies. (See the photo captioned, “Moth Caterpillar Protecting
Braconid Wasp Cocoon Stack”.)
On occasion, the caterpillar is linked to the cocoons with a bit of silk and hangs below the cocoon stack. (See the photo captioned, “Dead Unicorn Moth Caterpillar Protected Braconid Wasp Cocoons”.)
Some wasp larvae make a loose stack of cocoons and the caterpillar climbs on top of it and sits, protecting the cocoons, until it dies. Once again, these caterpillars no longer eat after the wasp larvae emerge. (See the photo captioned, “Duskywing Butterfly Protecting Braconid Wasp Cocoons”.)
As you walk along, you may see these tiny cocoons in the grass or on plants. (See photo captioned, “Braconid Wasp
Empty Cocoons”.) This is due to the fact that, after the caterpillar dies, it normally falls to the ground and isn’t noticed. The braconid wasp cocoons are attached to the item and do not fall, even after the wasps emerge from their cocoons.
If the wasps have emerged from their cocoons, the end of each cocoon has a hatch-type opening. (See photo captioned, “Braconid Wasp
There are predators for braconid wasps.
Ants will empty braconid wasp cocoons. (See photo captioned, “Ants Eating Braconid Wasps in Cocoons”.)
Another predator is a hyperparasitoid. There are species of chalcid wasps that parasitize braconid wasps, inside their cocoons. These wasps tend to exit from the side of a braconid wasp cocoon while braconid wasps emerge from the end of their cocoons.
Farmers and gardeners consider these to be beneficial insects.
They are responsible for the deaths of many Tomato Hornworm and Tobacco Hornworm caterpillars, enemies of tomato plants.