Where do silverspot butterflies lay their eggs?

Posted by: Alyse Kennamer, Zoo Corps intern

Oregon silverspot butterfly. Photo by Ryan Hawk/Woodland Park Zoo.

This summer, I had the unforgettable opportunity to work with a threatened species, the Oregon silverspot butterfly. While I was working here, an amazing idea came to my head for a study that could help scientists better understand and protect this species. I wanted to observe a female butterfly, see where she lays her eggs, and how it’s done.

Observing butterfly behavior in the silverspot lab at the zoo. Photo by Ryan Hawk/Woodland Park Zoo.

It all started at the beginning of the summer when I joined the silverspot project as part of the zoo’s teen program, Zoo Corps. I joined Zoo Corps in my sophomore year of high school, and am now enrolled in my first year of college. In early spring, we got to pick from a list of about 10 areas we wanted to work in at the zoo. Working in the lab where the zoo rears silverspot caterpillars was my first choice. You would probably think it was weird, why would a teenager want to spend her summer picking violet leaves and washing dishes for caterpillars when she was surrounded by a bunch of different animals? But I knew it would be interesting, and something I would end up loving. I was right about that.

Butterfly eggs set up in jars in preparation to  overwinter at the zoo, protected from the elements. Photo by Ryan Hawk/Woodland Park Zoo.

At the silverspot lab, it did indeed start with picking early blue violet leaves—the caterpillars’ sole source of food—and doing the dishes. But once I showed some initiative, I was able to do pupae processing, where we put the chrysalis into a triangular folded paper towel, and give it an individual number to send out to Oregon in an effort to rebuild the wild population. It was a lot of tedious work, but I knew I was saving a threatened species, and that was all that mattered.

Oregon coast habitat where Woodland Park Zoo has released silverspot butterflies. Photo by Ryan Hawk/Woodland Park Zoo.

In Mid-August, the silverspot team, consisting of myself, my Zoo Corps partner Autumn Olson, zoo collection manager Erin Sullivan, and zookeepers Lorre Myers and Diane Abbey, went down to Oregon for a release trip. While we were there, we saw butterflies galore. They were everywhere, and it was just so amazing. We even saw them mating, something Erin told us she had never seen in the wild before. One of the volunteers from the Department of Fish and Wildlife asked the question, “Where do the silverspots lay their eggs?” and nobody knew the answer, because it hasn’t often been seen in the wild.

I flashed back to the beginning of summer when I was starting my focus, when Autumn and I were told by our supervisor that she wanted us to do a project revolving around the butterfly. So I turned to Autumn, and whispered my idea to observe a female butterfly in the lab to see where she would lay her eggs. She thought it was great. That night over dinner we also got encouragement for the idea from Diane and Lorre, and then we knew we’d just have to get it approved by Erin.

An Oregon silverspot butterfly takes to a bloom on the Oregon coast. Photo by Rachel Gray/Woodland Park Zoo.

After we got back from the release trip in Oregon, we talked to Erin about it. She told us that it was a good idea, and even she wanted to know the outcome. Since the silverspot is a threatened species, we had to go through a lot of different approvals, including from the Department of Fish and Wildlife. The zoo receives butterflies into the lab in order to lay eggs, the basis for our conservation project, and each female has a target number of eggs we hope she will lay. On occasion there are some overachievers who lay more than the target number, and Fish and Wildlife gave me approval to use one of these overachieving butterflies for my project. The day we got the approval by Fish and Wildlife was the day I started set-up. Unfortunately, my focus partner Autumn couldn’t participate in the project because her school schedule wouldn’t allow it.

Enmeshed terrarium I created for the butterfly subjects of my study. Photo by Ryan Hawk/Woodland Park Zoo/

So it became my project. I set up a 20 gallon terrarium, and put rocks at the bottom of it, and then I did about ten trips to horticulture and filled a bucket up with soil to put into the terrarium. I put five early blue violet leaves into the terrarium, along with two false dandelion plants. After I did that, I built an upper part to the terrarium out of PVC pipe, so that if she wanted to fly she could. I covered that with mesh and secured it. After the terrarium was set up, I put my first female butterfly, whom I named Willow, inside the terrarium. 

Writing down my observations at the lab. Photo by Ryan Hawk/Woodland Park Zoo.

Now that the project is set up, I come in about three times a week, to work around my school schedule, and I watch and observe her actions. I make sure she has enough sugar water, and enough water. I take pictures, and some videos, just hoping, and waiting for the moment she lays an egg. Willow recently died, but she did leave me with one egg, which she laid on a violet leaf. This went with my hypothesis, which was that I believed the butterfly would lay eggs on the violet leaves because that is what the caterpillars eat. I have put the next butterfly, named Adunca, into the terrarium, and am continuing to observe her, to see what she does, and if I can catch egg laying on video.

I hope this study will shed light on the egg-laying habits of this threatened species, knowledge that scientists can use to help protect habitat needed for silverspot reproduction.