There are several species of solitary bees and wasps in our area, many of which nest in the ground. You can tell solitary species from yellowjackets in the ground by the entrance hole to their nests. Yellowjackets will generally have one hole that they use to come and go from, while solitary bees and wasps nesting sites will have many holes (they look like worm holes). Some are gregarious nesters with hundreds, sometimes thousands, nesting in the same area of ground. Solitary bees and wasps are all important pollinators or beneficial insects and should be left alone whenever possible. We have never seen a solitary bee that is aggressive. Below is more information on some of the most common solitary species we see in our area.
Mason bees are a solitary bee species in the genus Osmia. Just like all solitary bees, Mason bees are very docile and rarely sting even when handled. No worker bees in this species exist, as every female is fertile and makes her own nest. They typically nest in narrow gaps or naturally occurring tubular cavities. They do not excavate their own nests, but will utilize hollow twigs, abandoned nests of wood boring beetles or carpenter bees, or other small protected cavities. They are also readily attracted to appropriately sized nesting holes provided for them in drilled blocks of wood.
When mason bees emerge from their cocoons, the females mate with one or several males. The males soon die, and within a few days the females begin provisioning their nests. She gathers pollen and nectar and packs it into the base of her nest. She then backs into the hole and lays an egg on top of the mass. Then she creates a partition out of clay or mud or chewed plant tissue, which creates the back of the next cell which she deposits another provision mass and then lays another egg. This process continues until she has filled the cavity. Female eggs are laid in the back of the nest, and male eggs towards the front. Once she has finished with a nest, she plug sthe entrance to the tube and may seek out another nest location.
The sand wasps in our area are in the genus Steniolia. They are yellow and black with a banded pattern on their abdomen. The females dig burrows into sandy soil to rear their young. They specialize in catching flies to provision their nest burrows as their larvae grow. You will commonly see hundreds, sometimes thousands of these sand wasps make their nests in the same small, sandy area.
Leaf Cutter Bees-
Leaf Cutter Bees cut circular and oblong segments from leaves and use them to construct cylindrical tubes, about the diameter of a pencil divided into cells. Each cell is packed with a mixture of pollen and nectar and a single egg.
Mud Dauber Wasp-
Sceliphron caementarium gets its name from the Latin word "caementarius" which means mason, or builder of walls. Not surprisingly, these wasps build their nests out of mud! They typically nest in sheltered, shaded areas—Their nests are comprised of up to 25 vertically arranged, individual cylindrical cells which are then covered with more mud forming a smooth like appearance up to the size of your hand.
After building a cell, the female wasp captures several spiders. The captured prey are stung and paralyzed before being placed in the nest. A single egg is deposited on the prey, and then the cell is sealed with a thick mud plug. The larva spins a cocoon and pupates. Eventually the hatching larva will eat the prey and emerge from the nest.