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Ask The Entomologist question about digger bees

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Question:
I have something digging at the base of plants I have planted on a slope. It leaves a mound of dirt that resembles a fire-ant hill at the base of the plants. When I scatter the mound I do not see any ants as I do with anthills. I have seen some big bee-like bugs flying around the area and even saw one enter a mound. It appears that my plants may be suffering because of them. If they are there, and causing no harm, they can stay. If they are killing my plants, I need to know what I need to do to destroy or discourage them. I looked at “digger bees” and they seem harmless, but the pictures I’ve seen do not look like the ones in my garden.

Answer:
There are several species of ground-nesting bees and wasps.  The bees (digger bees) are all vegetarians and feed on pollen and nectar.  This, of course, is beneficial to plants because they help with pollination.  A digger bee female will dig a hole in the ground, lay an egg and then leave a wad of “bee bread” for the larva to feed on once it hatches.  Bee bread is basically a paste made from pollen and nectar.  The ground-nesting wasps have a very similar lifestyle except they are carnivores.  Instead of leaving bee bread, a wasp will provide paralyzed insects and spiders for their larvae to feed on.  The cicada killer wasp, for example, seeks out a cicada and stings it.  This paralyzes the cicada, which is then stuffed into a hole in the ground and an egg is laid on it.  The larva hatches and feeds on the paralyzed cicada, leaving the vital organs for last so that it doesn’t die and rot before it can be consumed.  A horrible fate indeed!  Other ground-nesting wasps will catch spiders and other insects, which may include plant pests.  So, the wasps will not harm your plants and actually may help them by removing potential pests.  These particular bees and wasps are solitary (although many may nest in the same area) and generally not aggressive.  Unless you accidentally step on one or catch one, they usually will leave you alone and not sting.  Sometimes you may see individuals hovering over the ground and chasing off other insects and animals that come near it.  These are males protecting the area, but they cannot sting.  They act big and bad, but are essentially harmless.  I’m not sure why your plants are not doing well, but I do not think it has anything to do with the ground-nesting bees or wasps.