Proof of concept: caterpillars spend time on tree branches

Today as I was watching the caterpillars feeding and I had a 'proof of concept' moment. Last summer I did a research project where I pinned artificial caterpillars (made of flour and lard) to branches of trees in the field and tracked the rate that they were attacked by birds. Specifically I was examining the extent to which countershading and eyespots protect caterpillar-like prey from bird attacks. See the published article here.

Aside: Countershading is a coulour pattern observed on many animals where those parts of the body that are naturals illuminated have darker pigment, and lighter pigmentation on those body sections that are naturally shaded. One of the main hypotheses for the evolution of countershading is that it makes it harder for predators to find prey because they blend in to their background better (i.e., it’s a form of crypsis). Hannah Rowland has done some great work on the adaptive value of countershading check out her publications and website. Here is a publication that used a similar design to the one I used:

Rowland, H. M., Cuthill, I. C., Harvey, I. F., Speed, M. P., & Ruxton, G. D. (2008). Can't tell the caterpillars from the trees: countershading enhances survival in a woodland. Proceedings of the Royal Society of London - B, 275(1651), 2539–2545

I made 4 types of caterpillars: solid green-no eyespots, countershaded-no eyespots, solid green-eyespots, countershaded-eyespots. Here are some photos to give you an idea:

 

I'll post more details about results of this work later, but one possible criticism of this design is that caterpillars may not spend a substantial portion of their time on tree branches. Arguably, caterpillars spend most of their time on leaves.

*Update: This work is now published, and I you can find out more in this more recent post. Also, the full citation for this work is below:

Hossie, T. J., Sherratt, T. N., (2012) Eyespots interact with body colour to protect caterpillar-like prey from avian predators. Animal Behaviour 84(1): 167-173, doi:10.1016/j.anbehav.2012.04.027

Today I observed 2 different caterpillars on the branch of the tree they are currently feeding on. I found the first one apparently resting on the branch, I spent some time watching it then eventually I decided to get my camera. When I got back it had moved to a leaf, but a few moments later I saw another one travelling along a branch. I don't have an SLR camera yet so without a manual focus on my digital camera it was hard to get good photos, but here are some:

Before observing this for myself, I had argued that caterpillars must spend at least part of their time on branches. How else could they travel between leaves? Despite this it felt good to observe it first hand, particularly during the day when many cryptic caterpillars are relatively inactive.