Looks like mud and dirt. Don't want to go poking at it if a swarm of killer bees fly out. Could use a garden hose from a few feet away.
Virtus_Probi said:I think that might be the mud dauber wasps that have the really thin section between the body and the abdomen...be careful!!
Id say mud daubers.
They are common here … never bother me … wasps are another story
Use water hose …