Butterfly Discovery at Eagles Rest

Upon discovering the caterpillars in July, I had forgotten that I’d seen several adult dotted blues earlier in the season. This one is sitting on barestem buckwheat (Eriogonum nudum) still in bud on June 4. 

In addition to all the wonderful flowers at Eagles Rest (see previous post, Eagles Rest Flowers Through the Summer), I had a good time watching insects visiting the flowers on my weekly trips, and just when I thought things were fading, I had a very exciting butterfly find.

When the first barestem buckwheat (Eriogonum nudum) flowers started to dry out and turn brown, I began to collect seed of it. The dried perianth (there’s no differentiation between sepals and petals) persists, so to collect seed, I just grab the dried stuff off the inflorescence and throw it in a bag. Since there was only a little ready to collect on July 16, I put it in a small envelope. When I got home that night, I spilled it out into a container to see if any decent seed had developed yet. Imagine my surprise when I discovered a small caterpillar clinging to the inside of the envelope! It was really lucky I looked in the envelope at all. Usually, I just put all the envelopes in a box and deal with them later.

Some lovely Columbia lilies (Lilium columbianum) attracted a pale swallowtail at the trailhead on July 2.

The caterpillar was rather slug-like—a gossamer wing in the family Lycaenidae! It appeared from the photos in Life Histories of Cascadia Butterflies that it was probably a dotted blue (Euphilotes enoptes) in its fourth and final instar. My first thought had been that it was an acmon blue (Plebejus acmon), but their caterpillars, though similar, are noticeably hairier. The host food plant of both species is Eriogonum nudum, and they are known to eat flowers, like many other lycaenids. Most other caterpillars seem to feed primarily on foliage. I was thrilled and couldn’t wait to get back to Eagles Rest to look for caterpillars on the plants. In the meantime, I put him/her on an Eriogonum inflorescence from my restoration in a small vase (covered so it couldn’t fall into the water) that I put in a large plastic storage box.

The pair of ants were tending the first caterpillar. It, like most that I saw, was probably in its last instar. I wish I’d known to check for caterpillars the week before.

Bumble bees were going crazy over a small population of Phacelia heterophylla on the lower part of the rock, June 4. The tall inflorescences provide plenty of flowers.

The following week, late afternoon on July 23, I went back to the lower part of Eagles Rest to look for more caterpillars. I headed off the trail at one of the first switchbacks onto the path to the base of the rock. I climbed up to the open area and stopped at the first Eriogonum plant to see if I could spot any caterpillars hiding in the flowers. A couple of ants were poking around the flowers. I remembered that some lycaenids are known to be tended by ants. Could they be hanging around a caterpillar? I put my glasses on for a closer look (I sure hate being so old that I can’t see anything without reading glasses anymore!) and carefully turned the cluster of flowers over to look at the underside. Sure enough, there was a red-and-white, slug-like caterpillar!! I watched the three of them for about 5 minutes. The ants moved around a lot, often both crawling on the caterpillar at the same time. This sure looked like a clear case of ant-tending to me! Apparently, these caterpillars exude a bit of honeydew liquid when the ants stroke them. The ants enjoy the treat, and, in turn, they protect the caterpillars from other insect predators—a wonderful symbiotic relationship.

The second caterpillar was a pale green.

I couldn’t believe I found a caterpillar on the first plant I checked. I really don’t see butterfly caterpillars very often, and I’d only seen a few lycaenid caterpillars in my lifetime (see A Sea of Blue at Maple Creek Meadow for the most recent before this). Was this dumb luck or were there more? I checked the second plant, just a couple of feet away. There was a pale green caterpillar! Five minutes later, I saw something dark partly hidden in a cluster of flowers—another ant. I was sure there must be a caterpillar nearby. It took a bit of searching, but I finally spotted it deep in the flower cluster. This one was a pale pinkish color—perfectly camouflaged. Only the ant gave it away!

This little one might have been in its second instar. It is very small and still has a black head.

After looking through countless more inflorescences, I eventually found another 4 or 5 more caterpillars, though I never saw any more with ants. They varied in size and color. Perhaps they change color during the different instars (stages) to help hide them match the flower color as it ages. The last one I found was pink and red—easy to spot on fresh white flowers but much harder to see on the fading brownish pink ones. There were more Eriogonum plants in the area, but many were out of reach on steep rocks. It was also getting quite late in the evening (7:30pm—I was also getting hungry!) so I decided to call it a day.

On my way back to the trail, I stopped again to see if the ants were still accompanying the first caterpillar. It was over an hour after I’d first spotted them, but, although not on the same flower cluster, all three were still together on the same plant!

The last caterpillar I found was the most beautiful. It is really interesting how variable their coloration is. Caterpillars of other species like monarchs and swallowtails change from stage to stage, but the individuals of the same age are more or less identical. Other gossamer wing species, however, also have caterpillars vary quite a bit, like the gray hairstreaks I saw on my way to Maple Creek Meadow in June.

Sadly, the caterpillar that snuck home with me in the seed envelope didn’t make it. It ate for a few days before crawling under some paper to make its chrysalis. But instead of transforming into a chrysalis, it just shriveled up. However, I brought home another caterpillar the following week. It is now overwintering in the same container after successfully metamorphosing into a chrysalis under a layer of paper at the bottom of the container. They know how to stay hidden and protected. I do hope it survives the winter and hatches into a lovely dotted blue next spring. And next year, you can bet I will be looking carefully at every Eriogonum I see!

One Response to “Butterfly Discovery at Eagles Rest”

  • Blanche Douma:

    That was a wonderful story, Tanya. You provided me with visions of beauty on this dreary, cold, and wet day. Thank you so much.

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