Black Swallowtail Butterfly: Check That Dill Sprig Before You Pick

Black Swallowtail Larva on Dill

Black Swallowtail Larva on Dill

I went out to my herb garden to pick a few sprigs of dill to brighten up some of last summer’s corn chowder that I had defrosted for lunch.  As I bent over my patch of dill I noticed a Black Swallowtail Butterfly larva munching away.  Looking over the little patch I saw two more, all in what seemed to be the fourth stage of development (called an instar).  The life cycle of a Black Swallowtail Butterfly is fascinating.  The eggs are not obvious and the first noticeable instar is when the larva molts into a worm-like creature that is black with a little white ring around the center.  The following instar is an orange and black prickly looking caterpillar and then comes the instar I am seeing.  They keep this general form and coloration until they grow to be 3 to 4 inches long.  At this point they form a chrysalis and after a couple of weeks, the butterfly emerges.  As the caterpillars grow they become more and more noticeable and can fall victim to birds.  If you want to observe the miracle of metamorphosis you can take a caterpillar inside and watch it happen.  This is especially fun for children.  You will need plenty of the host plant you found it on to feed it until it forms its crysalis, some branches so it will have something to attach the crysalis to and a safe place like an aquarium, a large jar or a fish bowl.  Put screening over the top so air can get in and the butterfly can’t get out until you’re ready to release it.  Other host plants are parsely, carrots, fennel and other members of that family.  It will take two to three weeks once the crysalis has formed.  Be sure to release it as soon as it can fly.  Don’t try to help it leave the crysalis.  It needs to do this job itself to gain strength.

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