It has recently become rather popular to use artificial plasticine caterpillars to measure predation rate by insectivorous predators. These caterpillars are also called as clay caterpillars or dummy caterpillars. The most common materials have been soft (unedible) plasticine or (edible) dough.
It is rather easy to identify that a caterpillar has been predated, meaning that it has pecking, biting or scratching marks. But identifying the predator can be more challenging. I give here some examples. This is no way a comprehensive list. These are photos I have taken of the caterpillars used in my experiments in Finland and in Papua New Guinea. The photos are not all that great quality. I have taken them in forest while doing the fieldwork with a small (waterproof) camera.
In my experiments in Finland birds were the only predators. I probably could have also identified parasitoids, but realised that after the experiment. The marks left by parasitoids are just small needle-size holes. So, these three photos are all caterpillars predated by birds. Usually the mark has a clear beak shape.
Papua New Guinea
In tropics the list of possible predators is much longer. But there is also literature of what the different predator marks look like on plasticine caterpillars (Sam et al. 2015 Ecography). Based on that article we could identify birds, ants (bigger and smaller), crickets (sorry, no photos here) and spiders. We also had once a mouse as a predator.
Birds can leave all kinds of different marks, depending on their size and predation strategy.
This caterpillar had on one side marks by bird and on the other side by ants.
Ants can be usually separated to bigger (distinctive bite marks) and smaller ants (general chewing).
Spiders munch only the surface of the caterpillars.
This mouse left quite clear tooth marks on these two caterpillars which were close to each other on a branch.
UPDATED 23 May 2019
Bastien Castagneyrol and Elena Valdés-Correcher kindly provided me photos of plasticine caterpillars that have marks left by something else than predating animals (branches, leaves, fingers etc). Usually these are rather easy to recognize. In Papua New Guinea I noticed occasionally that if the weather had been sunny for few days, the plasticine starts to dry and easily breaks. Sometimes these cuts on plasticine can look a bit like predation marks.
© Elina Mäntylä (firstname.lastname@example.org), 20 May 2019