Butterflies engage in a behavior called “mudding” or “mud puddling”. They visit areas with wet sand or mud and drink.
There seems to be a social element to this activity because the butterflies tend to form small groups that are clustered together. If there is more than one species present there are usually species groups, rather than randomly dispersed individuals. If something spooks the group, they have a tendency to land back in an area that already has butterflies.
The butterflies are doing something besides just obtaining water. Often they will expel drops of water from their rear ends.
It has been observed that approximately 90% of the butterflies that are mudding are males, and scientists speculate that the males transfer minerals to the females and their offspring during mating.
I always find the groups fun to watch. There is something social going on, but exactly what is hard to define.
Sunday after a brief rain I walked the gravel road near my home. I saw some butterflies mudding near the body of what seems to be a road-killed butterfly.
Here we have a little yellow, Pyrisitia lisa, a live clouded sulfur, Colias philodice, and a dead clouded sulfur. The live butterflies were not bothered by the remains of the non-living butterfly. They did not seem to scavage from it, but ignored it while mudding. However, butterflies that flew by seemed attracted to the grouping.
There was at least one other dead clouded sulfur on the road. Mudding groups seemed to be near the bodies.
It seems to me that when butterflies engage in mudding behavior they are attracted to other groups doing the same. The dead butterflies act sort of like duck decoys, attracting those individuals that fly by.
It might be fun to try to devise an experiment to prove that.