In this paper from Conservation Biology, researchers counted what proportion of mud snails were bedecked with a trematode cyst that, as an adult, parasitizes terrapins. They felt this would be easier than directly counting diamondback terrapins on the Georgia coast. It has got to be a lot easier to ID a diamondback terrapin than a specific species of trematode cyst, but still, a very cool idea with the potential to be used in other hard-to-survey species.

Photo courtesy of the US Fish and Wildlife Service