While walking in a state park in New Jersey last week, my husband and I came upon what looked like anthills. This small sign was posted on a nearby tree: "Please don't step on the mounds of dirt. Miner bees are at work below!"

We generally avoid anthills anyway, so as not to injure the ants. As far as we know, though, this is the first time we've run across Miner bees. In what ways do they differ from other bees?