Chalcid wasps in Black Swallowtail butterfly chrysalises

How can I tell if my chrysalis is infected with chalcid wasps?

Before wasps emerge from the chrysalis, the abdomen will slump if it is held up in the air. The wasp larvae have killed the chrysalis. The muscles that hold the abdomen segments together are either dead or eaten by wasp larvae.

If you gently push the abdomen of an older chrysalis to the side, it should move back into place. If it is infected with wasp larvae, muscles will not be able to move it back into place. The abdomen will stay where you push it.

A healthy chrysalis will have light membranes between its abdominal segments. As wasps grow inside the chrysalis, the membranes turn dark.

Infected chrysalises turn darker and often have a reddish tinge to them.

Remember! When a chrysalis is first infected (eggs laid in the chrysalis) it will appear healthy, have the correct colors and shades, and will move normal. Once the wasp larvae have grown for a few days, the color of the chrysalis will darken.

A chrysalis that has a mature butterfly inside it will also turn dark the day before the butterfly emerges. If a butterfly is inside, you will see the wing pads the day before the butterfly emerges. If it darkens and wing pads cannot be seen, it is a danger sign.

If you aren’t sure, simply place your chrysalis in a large clear cup with a paper towel down one side and across the bottom. Seal it tight. If a butterfly emerges, all is well. If wasps emerge, you can freeze the cup for several days before disposing of it. They may live over a day in the freezer.

Click on this sentence to see a YouTube video with some of this information in “How to tell if a swallowtail chrysalis is alive.”

Click on this sentence to see a video showing how to tell if a swallowtail chrysalis is infected with chalcid wasps.