Raising Black Swallowtail Caterpillars in Your Garden
Have you ever witnessed the complete lifecycle of a butterfly firsthand? If you haven’t, it is truly the most marvelous and awe-inspiring experience. To see a teeny tiny egg slowly (but not as slowly as you’d expect!) transform into a butterfly truly feels like a miracle. You can buy black swallowtail caterpillar eggs online, but there is a very fun way to simply attract butterflies into your garden to lay eggs.
The past two gardening seasons, I’ve had the pleasure of “raising” black swallowtail caterpillars into butterflies. The first year it was by chance when I found some small caterpillars on my dill plant. This year, I intentionally grew a lot of dill in hopes it would happen again and so far I’ve had over a dozen caterpillars.
Do you want to have black swallowtail caterpillars in your garden? Here’s what you need to know.
Plant host plants
Butterflies seek out what are called “host plants” to lay their eggs on. Host plants are the plants that the caterpillars are evolutionarily matched with to sustain them until they become butterflies. Many caterpillars can’t and won’t eat plants that aren’t their host plants, just like we can’t (they don’t have the nutrients we need) and won’t eat dried leaves. The butterflies only lay their eggs on these plants because the caterpillars need food readily and plentifully available when they hatch from their eggs.
For black swallowtail caterpillars, their common garden host plants are dill, carrots, fennel and parsley. I have grown all three and every year they first lay eggs on my dill, then on my parsley once the dill is stripped or dead. This seems to be true for all of the gardeners in my area; however, I have seen other gardeners online have success primarily with the other two. It depends on a lot of factors, so I would recommend growing a bit of each, stay watchful and figure out which host plant the swallowtails in your area prefer.
Note: It’s important to purchase organic plants or start them yourself from seed.
Plant them somewhere that you can ensure will have no pesticides whatsoever. Avoid planting them near neighbors yards that are sprayed. If you use pesticides – even organic ones such as neem (which I don’t recommend) – plant these plants far away from anything you use the pesticides on.
Attract the Black Swallowtail Butterflies
Another important factor is having flowers in your garden to attract the butterflies in the first place. Even if you don’t want to raise caterpillars, I would always encourage any gardener to grow flowers to attract and support pollinators of all types. But if you aren’t yet, plant some flowers!
Make a plan for if/how you will protect the caterpillars
Once your eggs hatch, you have three options: bring your caterpillar inside and care for it in a butterfly enclosure, cover the plant somehow, or leave it to nature. Here are the pros and cons of each:
1. Bringing your caterpillar inside
I have done this in the past and it works, but is not my preference. This option is highly secure from predators and allows you to watch your caterpillar grow most easily. Butterfly enclosures are fairly affordable and will last a very long time.
I don’t prefer this method because of the responsibility of caring for the caterpillars and keeping them fed. Plants wilt quickly and the hungry critters don’t like wilted foliage. To remedy this in the past, I have purchased a plant start from the store and put it in the enclosure with them in it’s pot. The plant stays alive with a bit of watering and the caterpillar has fresh food as long as you keep the plant alive.
2. Covering your plant
This is the option I go with because I can’t handle the heartbreak of losing a caterpillar but I still like to keep it more natural. It’s downsides are that this method is the most work and it requires a little creativity. If your caterpillars are on fennel or dill, I recommend putting a tomato cage over them and covering it with some meshy fabric. If your caterpillars prefer parsley or carrots, the cage may be too tall and narrow. I would put a stake in the center of the area and create a tent by laying a piece of meshy fabric over the area and securing it with small stakes or rocks. If you go this route, I recommend putting sticks vertically under the enclosure. The caterpillars want a sturdy place to pupate and will likely try to escape the enclosure if they can’t find one.
3. Leaving it to nature
If you are like me and will be devastated if your caterpillars don’t make it to butterfly-hood, I would avoid this. If you are okay with the risk and would prefer to keep your to-do list short, this is a great option. All you have to do is let the caterpillars do their thing and hope that the predators don’t find them!
Watch them grow and pupate
When the eggs first hatch the caterpillars will be smaller than a grain of rice. In 7-12 days they will grow to be roughly as large as a penne pasta noodle! When it’s time for them to start their process of becoming a butterfly, they will crawl to a high point on a stick and curl into an upside-down ‘J’ shape with their head pointed up. Within hours they will have become a chrysalis and now all you have to do is patiently wait!
The length of time the black swallowtail caterpillars are in their chrysalises can vary a lot. Some may even overwinter and emerge in the spring. Don’t worry about them in the cold; they were made to survive the snow and freezing temperatures. If it is early in the summer, you should see them sometime in 7 – 20 days. If they haven’t emerged when you think they should have, just be patient! Sometimes something will go wrong while they are in their chrysalis, but I would avoid disturbing them because they may just be slower than average.
Send Them Off
Once the butterflies do emerge, they will need to dry their wings, which are crumpled from being in the chrysalis. When they are ready to fly they will start fluttering all over the enclosure. If you are using an enclosure, let them out as soon as you are able. If you think you won’t be around when they emerge, leave a little opening before you leave for them to get out of.
It’s purely exciting and rewarding when you get to witness them emerging and flying off as butterflies! You have now seen as much of the butterfly life cycle as you can and what a beautiful thing to experience.
Don’t Worry
I have had my fair share of worry over my black swallowtail caterpillars and after a lot of research and experience, I still don’t have all of the answers. Here are the most common questions though, and all of these weird behaviors are perfectly normal.
Why isn’t my caterpillar moving?
It’s probably sleeping! Caterpillars are a lot like human babies; their main activities are eating and sleeping. It’s a lot of work growing so quickly!
Why did my caterpillar excrete a lot of green liquid?
This can be highly alarming when you are used to their small, round frass. Don’t worry though; a lot of times the caterpillars will do this to prepare their bodies for pupating. It likely means they are going to be a chrysalis soon!
Why does my caterpillar look shriveled?
This is also very normal for caterpillars. They grow very quickly, so they need to regularly molt, or shed their skin, in order to fit their chubby little bodies in their skin. If you are lucky enough to catch one molting, take a minute to observe. It’s a cool process to see them crawl out of their skin!
My caterpillar is frantically crawling around the plant and won’t stop.
This is another sign that they are getting ready to become a chrysalis. They are looking for the right place to pupate and sometimes it can take them a while. They may end up crawling away in search of somewhere they deem more secure, so don’t be surprised if you can’t find them later. If they are trapped in an enclosure, eventually they will settle into a place and begin pupating.
Having caterpillars is one of the many joys of having a pollinator-friendly garden and I hope you are able to enjoy witnesses a small slice of nature in your own yard. Happy gardening!
