Tohickon Creek and the Sleepy Orange
- Sam Makler
- Jan 25
- 3 min read
Updated: Jan 26
When going out on botanizing trips it's always a great deal of fun searching for butterflies that are associated with the plant communities you are in. In grassy meadows I tend to think about skippers and the grasses they use as host plants. What sedges are here? What grasses? These are questions I often find myself asking in most herbaceous plant communities. On the other hand, sometimes you see butterflies you are not expecting at all! Here's a story detailing exactly that.
I was wading through the Tohickon Creek in mid-August looking for some specific sedges and to my surprise saw a cloud of sulphur butterflies above a gravel bar that ran parallel to the creek. I could tell right away that this was the biggest population of sleepy oranges I had ever seen. Sometimes you will see the closely related orange sulphurs or cloudless summer in groups but almost always they are alone flying through grassy landscapes. Seeing 3 or 4 yellow/orange butterflies was interesting, and as I waded closer I could see the stand out orange color and black markings that verified it was in fact sleepy oranges. Intermixed between the blooming cutleaf coneflower, small black willows and sycamores were flowering american senna, the sleepy orange’s host plant. This was a small plant community that was supporting a happy, healthy and robust population of this amazing butterfly!
I ended up counting 9 different sleepy oranges all quickly flying to and from different senna plants. They are one of the most difficult butterflies to photograph as they will stay on the wing for very long periods of time. They also seem to detect movement from far away exceptionally well. As you stand there watching them fly for 5 minutes hoping to get a picture, they will finally take a break on a rock and invite you in. The second you make a move towards them they’re off again!
These little gravel bars and streamside plant communities are amazing. They have a a wide array of plants found within that always varies from one location to another. More often than not you can find them supporting plant species with conservation status ranks. The composition is strongly dictated by water flows and the sun and shade from the riparian plant communities. The substrate produced by the adjacent water source is also another major determining factor. Sometimes this is fine sand or larger stone. In another post I will talk about some of the neat plants found along larger rivers in similar communities
Unfortunately many creeks and smaller tributaries in SE Pennsylvania will have highly eroded stream banks and edges that are caused by huge surges of stormwater from surrounding development. This degradation ultimately leads to the loss of these special plant communities and in turn the loss of insect species who depend on the plants that would be found within. Seeing the streamside community along the Tohickon doing so well and supporting such a robust butterfly population indicates a certain level of controlled storm water management and stream health. It’s exciting to see!
In managing a site like this it would be crucial to monitor for encroaching invasive vegetation that often does very well in these conditions. Purple loosestrife can often be found intermixed in these communities. That is easy to monitor for and if you are uncertain with plant ID you can wait for the distinct purple flowers to appear in the summer. Other invasives like Japanese knotweed are much harder to remove from spaces like this and can quickly replace the entire composition. In just a few years one shoot of Japanese knotweed could overrun the whole section here and would in turn wipe out the incredible plant diversity and insect diversity that is so interconnected.
If you find yourself around a creek or wading through, take a look around the edges of the water! In many cases you may find butterflies, birds and plants you will not find anywhere else.