As I was planting some veggies yesterday, I saw a female Black Swallowtail butterfly in her characteristic search and hover mode as she investigated various plants in the garden. I knew from this fluttery flight behavior that she was searching for the right type of plant on which to lay an egg (aka host plant). As with many species of butterflies and moths, Black Swallowtail females tend to be discerning when it comes to which plants they choose for their eggs. Host plants of the caterpillar include members of the parsley family (Apiaceae) including Carrot, Parsley, Dill, Fennel and Queen Anne’s lace and some members of the Rutaceae such as common garden Rue (Ruta graveolens).
I have four of these in the garden right now: Parsley, Bronze Fennel, Sweet Fennel, and Rue. From my experience, the Bronze Fennel seems to be the preferred host, especially early in the season. The tops of the Carrots I grew last year were also very popular with the caterpillars. As any herb gardener knows all too well, Parsley is also immensely popular as a host plant, with the larvae often totally denuding your herb supply if you only have a few plants. That is one reason I plant the fennels as they tend to get tall (3 or 4 feet) which is usually enough to provide an adequate food supply. Rue becomes especially important as a host plant in my garden in the late summer and early fall as Black Swallowtails complete their final generation before winter. Last year I had one large rue plant with over 20 caterpillars on it and rue tends to be less completely devoured compared to some of the other hosts. Rue stems also tend to sprout quickly after being eaten. But I have also read that Rue can cause skin irritation in sensitive people, so be cautious if you plant it.
Naturally, I was excited to see what I thought were the first butterfly eggs of the season in the garden. I grabbed my camera and took a few shots after finding eggs on several fennel and parsley plants. The eggs are spherical and cream-colored (or slightly yellowish). The other swallowtail species eggs I have seen are also spherical although different species tend to have different colors. The eggs of other butterfly and moth groups can be quite ornate with many shapes, colors, and ornamentations (perhaps a blog topic later this season). Each butterfly egg is surrounded by a hard outer shell, called the chorion, to protect the developing larva. The shell is lined with a layer of wax, which helps keep the egg from drying out. There is a small opening near one end called a micropyle, which allows sperm to enter the egg for fertilization. The egg shell also is dotted with microscopic pores called aeropyles which allow gas exchange. The butterfly glues the egg to the plant leaf using an adhesive-like substance produced in the colleterial glands. Black Swallowtails lay the eggs singly (generally on the top of leaves) although she may lay several eggs on the same plant.
As I wandered the garden looking for more eggs, I realized the one I photographed is not the first of the season…I found a tiny caterpillar on one of the Rue plants. Since it takes 3-5 days for these eggs to hatch, I had apparently missed a few from the past weekend.
This is what is known as the first instar larva, the stage after emergence from the egg. It looks quite different from how this species is pictured in most caterpillar field guides. As is common with many species, Black Swallowtail caterpillars undergo a noticeable change in appearance as they molt five times on their way to becoming a chrysalis. This early stage is considered a bird poop mimic, with a dark background color containing a whitish splotch, just like a bird dropping. Many other species have this basic color scheme, especially as early stage larvae.
I’ll hang onto this little guy and try to photograph it as it develops over the next couple of weeks. I think I’ll have plenty of opportunity to get the various life stages as I found 11 eggs (and two more first instar larvae) on one Bronze Fennel plant this morning. While searching the Internet for a few details on these eggs, I found what could be my moneymaker in retirement – seem like a few companies sell butterfly eggs for people to raise and I saw one site that had Black Swallowtail eggs for $2 each! If I had the time and inclination, it could be a busy (and profitable) summer.
Did you ever start a side Hustle with the black swallowtail? I currently have about the same amount of eggs, with 9 that are already hatched and 2 that already went into chrysalis, with one emerging already and the other might go through the winter. I bought a cage and some more parsley with dill and brought the little hatchling in from their piece of parsley. I was wondering since they haven’t moved much, how long do they stay in this stage. What happened with your little hatchling as he grew. I only know once they get into the final 2 stages. Any advice will help greatly. Thanks!
Hi Michelle. I have raised them in cages with cuttings from my garden plants or potted plants purchased at nurseries. Occasionally we have used parsley from the grocery store but that must be washed thoroughly (in case of pesticides) and I prefer to use store-bought cut parsley. Caterpillars are often motionless for a day or so when getting ready to molt. This is a great reference on their life cycle – https://entnemdept.ufl.edu/creatures/bfly/bfly2/eastern_black_swallowtail.htm. I place sticks in the cage and hope they form the chrysalis on those rather than the sides of the mesh cage. Hope this helps and good luck!
Thank you for the quick reply. We first noticed these beauties last year when we first got our parsley potted plant, which grows wonderfully and is so easy. We had 5 in the plant we first noticed last stage before chrysalis. 3 left before we could find a cage to put them in. We grabbed the last 2 and we had to reattach one on a stick with very small amount of a hot glue gun, which my partner did an amazing job of replicating what they do. I would be too clumsy lol. They went through the winter and emerged in beginning of May this year. We got another plant, and oh my….this one female comes by everyday to lay eggs. We have 3 batches already. Sadly, my cage isn’t big enough to house all of them. Trying to find a good cage is hard. Thank you for the link, I have not read this one yet and it was a good share. 😊
I purchased many cages from BioQuip but, sadly, they closed this year. This link shows what looks like an identical cage to what I have – https://www.amazon.com/Trasfit-Pop-up-Butterfly-Habitat-Terrarium/dp/B01LN8ETBS/ref=asc_df_B01LN8ETBS/?tag=hyprod-20&linkCode=df0&hvadid=312153111586&hvpos=&hvnetw=g&hvrand=1331422001740335586&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1027215&hvtargid=pla-571712360108&psc=1
I was going to get one of those, but at the time we only had a couple. I bought a little reptile cage with a screen around, except for the front door. Now we have so many, this has become a cool project for hubby and I. We went to lowes and we are going to build a bigger one about 32 length to 18 height 10 deep. It will fit 3 Potter plants. Which even cooler we bought some more parsley, dill and low and behold there were baby black swallowtail on them to the additional we already had lol. Now I know how we got them to begin with. I lived at my place for 13 years and we never saw any. Crazy cool. https://www.chewy.com/zoo-med-nano-breeze-reptile-cage/dp/344869?utm_source=google-product&utm_medium=cpc&utm_campaign=12737201938&utm_content=Zoo%20Med&utm_term=&gclid=Cj0KCQjwmdGYBhDRARIsABmSEeO09Bxs4-sms9tGCgIWlxn8McLfcp36lPrPI8LAtxet3Yg__48L04gaApYSEALw_wcB