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Needle in a Haystack

Black swallowtails found my parsley again

4-Minute Read

I love parsley. Usually I try to plant a few parsley plants every year, but generally it ends up being no more than a handful of plants. This year, I managed to overwinter one single mature plant and have a few additional tiny seedlings. Despite only having one properly sized plant that could even possibly support something eating it - she found it. The Black Swallowtail found it again.

Black Swallowtails, Papilio polyxenes, are in the butterfly family Papilionidae (aka, the swallowtail family). Every year it seems, they manage to find my few solitary plants. We have TONS and tons of other suitable host plants on the property. Like dill, celery, carrots, fennel, and the Queen Ann’s Lace that grows like a weed everywhere here. And I mean everywhere. Its pretty, so I like it, but it gets in all my garden spaces and chokes out my other plants, so I usually have to go and pull them out. I’ve never found a black swallowtail caterpillar on any of the hundreds of Queen Ann’s Lace plant and seedlings I’ve pulled out. Only on my parsley plants.

Usually I try to rehome the Black Swallowtail caterpillars I find. Like to the Queen Ann’s Lace located absolutely everywhere else. Last year I gave several to one of my colleagues whose daughter has a butterfly-rearing house. Generally when I find one caterpillar, I find several. After a thorough check of my plants, there’s only one caterpillar this year… Its already so big that it must be close to spinning it’s chrysalis. Maybe I’ll leave this one on my poor parsley… How much more could it possibly eat at this point?

Black Swallowtail caterpillar on my parsley

I just couldn’t help myself. Before leaving the garden I decided I had to pet the caterpillar. Swallowtail caterpillars have this really fun defensive action when disturbed. They temporarily extrude bright orange colored horn like things called osmeterium. In conjunction with rearing their heads, the osmeterium are supposed to scare away predators and to emit a foul odor (although I didn’t smell anything with this one) to discourage being eaten. I’m afraid it had the opposite effect on me - the only reason I disturbed the caterpillar in the first place is because I wanted to see its bright orange horns….

Black Swallowtail caterpillar showing its osmeterium
Black Swallowtail caterpillar after I left it alone again

Here’s a video of me gently petting the caterpillar to get it to show its osmeterium… Enjoy :)

Round two

Post update 08/06/2021

Well, for the first time, I’ve now found Black Swallowtail caterpillars on my celery plants! I wasn’t expecting a second generation this season, but apparently they do often have two generations in northern states. Southern states sometimes get three generations!

This time I’ve found much younger caterpillars. It’s kind of amazing how different the young ones look from the older ones. Ok, maybe not that amazing considering they do turn into butterflies lol. I’ll update the post if I manage to get a photo of one of the adults. So far I’ve only seen the caterpillars, but that means the adults must have been here at some point… I wonder why this second generation went for my celery instead of the parsley they usually seem to prefer at my house? I have a hypothesis, but nothing to back it up with so I’ll keep it to myself for now.

Young, 2nd generation, Black Swallowtail caterpillar on my celery

If you want to learn more about Black Swallowtails check out:

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Written by an entomologist for the enjoyment of all... The goal is to post 1 new story every week or so. Stay tuned!