Lovely tiger swallowtails feeding on fresh raccoon poo (taken a few years ago in Hunterdon Co., NJ). This behavior apparently allows butterflies to gain extra nitrogen and sodium which are needed for reproduction and are scarce in their typical sugary fare of flower nectar (Lederhouse et al. 1990). These nutrients can also be found in rotting animals (scroll down on this link to see one eating a dead raccoon!) and also puddle margins. I've seen great clouds of them gathering on the mud of drying ponds - it can be quite spectacular!
Here is a red admiral drinking nutrient soup from the manure on an amputated lamb's tail (the tail had been "docked"). (Photo taken a week ago in Warren Co., NJ.)