While visiting a local park this week, I stopped by to visit a Pogonomyrmex nest I have been watching over the years.
I almost immediately noticed the black spots around the nest entrances.
Here's another entrance about 20 inches from the first two. There was a noticeable blackening around the hole in comparison to the surroundings. Otherwise, the ants seemed to be active and doing fine.
This is a closer view.
Looks kind of shiny.
My first thought was ant feces. Studies have shown that some ants mark their nest areas with feces, for example a study by Grasso et al. (2005).
My other guess is that someone tried pouring something into the nest (as it is a public place.)
What do you think? Have you seen this before?
Grasso, D. A., Sledge, M. F., LE Moli, F., Mori, A., and Turillazzi, S. 2005. Nest-area marking with faeces: a chemical
signature that allows colony-level recognition in seed harvesting ants (Hymenoptera, Formicidae). Insectes Sociaux 52:36–44. (.pdf available for viewing)