Black Swallowtail (Papilio polyxenes) caterpillars have popped up here on the B&B blog before. One blogger found them all over her parsley plants last year, and I wrote about the butterfly’s life cycle myself around the same time. With summer and caterpillar season just about here, I thought a little refresher on what these caterpillars look like and where to find them might be useful so butterfly gardeners know what to look for.
This is one of my favorite butterfly caterpillars, in part because it changes its appearance so many times during its very short lifespan. Let’s start at the beginning…
- The eggs look like very small white, cream, or light green pearls.
- The freshly-hatched caterpillars are black with a white stripe around their middles. Note that in the photo below, the upper-most caterpillar has been eating its eggshell; most caterpillars consume their eggshells right after they hatch for the nutrients they provide.
As caterpillars begin eating, they also begin growing. Soon, they grow too large for their skin and have to shed it (called molting), and the phases in between molts are called instars. Most caterpillars will go through five instars before they molt one final time into chrysalis. This process generally takes about two weeks.
While many caterpillars look similar as they grow and pass through different instars, the Black Swallowtail has some distinctly different outfits in its closet. Instars one and two look very similar, but by the time we get to three we can see some changes as more colors and patterns start to emerge.
If that change isn’t enough for you, check out the fourth instar caterpillar, shown below.
The caterpillar is a pretty good size by now, but it has one more major change (as a caterpillar) to undergo. The fifth and final instar looks quite different from any before it.
Black Swallowtail caterpillars not only have a lot of outfits, they also have accessories and their very own “perfume”. When scared or agitated, Black Swallowtails force out an osmeterium from their heads. This fleshy appendage is covered with very pungent- smelling goo, which scares off predators (but is completely harmless to humans).
And now, of course, the caterpillar is ready for its most amazing transformation of all. It wanders off to a safe place, hangs in the traditional “J” shape (this one might look more like a “C” as, like most swallowtails, they secure their mid-section with a second piece of silk), and sheds its skin one final time to form a chrysalis (also called a pupa), where they rest for ten days or so while the butterfly forms inside. (Learn more about that process here.)
Interested in attracting these amazing creature to your own yard?
- They’re most common east of the Mississippi, but can be found as far west as California and the southwest, though not in the Northwest. (See a spottings map here).
- If you live in their range, all you need to do to attract them is to plant their host plants, which include just about anything in the Parsley family (Apiaceae), especially parsley, dill, and fennel. They’ll also use Common Rue (Ruta graevolens). Plant a large patch of one or more of these, and Black Swallowtails will find you.
- This is really fun for kids, as both the caterpillars and the host plants are completely safe to handle (although please supervise young children – caterpillars are pretty fragile).
Do you have Black Swallowtail caterpillars on your parsley (etc.) yet? Tell us where you are and when you first spotted them in the comments below!
Oh, and in case you were reading down through to the end of this post just to find out what the butterfly ultimately looks like… well, this post is about caterpillars. If you want to see the butterfly, you’ll have to click here.