Solitary Bees

Solitary bees are making their nests in the stump of an orange tree utilizing what appear to be abandoned beetle borings.

These tiny pollinators are always hard at work gathering food for their offspring and, when the time comes, collecting material that they use to seal the entrances to their nests. 

I suspect that these bees are Megachile (Subgenus Chelostomoides) bees because they look like ordinary leafcutter bees but don’t seem to be cutting or carrying leaf fragments to their nests, and they seal the openings of their nest cavities with resin and occasionally other organic material (leaf paste, grass blades, wood) and (possibly) sand and tiny pebbles.