Chalcid Wasps (Monodontomerus & Pteromalus venustus) - Body Snatchers
Characteristics: Mono species are widespread throughout North America, and all are metallic green, blue, or black, with red eyes, and are 5/64 to 5/32 inch in length (~2 to 4 millimeters). Males are slightly smaller than females.
P. venustus females average up to 7/64 inch (~2.5 millimeters) long. Females are black with dark brown legs. Males are similar in size but have metallic green heads.
Chalcid wasps are some of the most destructive parasites of mason and leafcutter bees. This group includes both native (Monodontomerus) and nonnative (Pteromalus venustus).
The sneaky female wasp invades nests through small openings or weak spots in the nesting materials or through incomplete or uncapped nesting holes. They use their needle-like ovipositor to paralyze the bee larvae by inserting it through the cocoon wall. Females can attack multiple cocoons, so loose cocoons are particularly susceptible and must be protected!
After paralyzing the bee larva, the female lays 10 - 50 eggs inside the cocoon. Upon hatching, the wasp larva consumes the bee and completes its development inside the cocoon undetected. The wasps emerge as adults from the cocoons by chewing a small hole in the side. These wasps develop very fast, so multiple generations can develop each season.
What You Can Do:
1. The most critical control method for Chalcid wasps is the use of solid nesting materials free of entry points, especially at the back of the nest. Nesting materials without backs or that are too thin are easily penetrated by Chalcid wasps. Read our Bee-Safe Nesting Materials article for more information on nesting materials.
2. Mason bee cocoons that did not emerge within a few weeks of release may be full of parasitic wasps and should be destroyed.
3. Mono wasps are often most active towards the end of the mason bee season. Therefore, completed nests should also be removed from the field and stored in a BeeGuard Bag or another breathable mesh bag at the end of the nesting season. Occasionally check the bag and kill any adult wasps that may have emerged.
4. Small batches of mason bee cocoons can be hand sorted to remove chalcid wasps. Parasitized cocoons will feel softer than healthy cocoons and appear almost empty when squeezed lightly. You can store questionable cocoons separately in a breathable, transparent container. Check the container often and destroy any parasitic wasps that emerge.
Sapygid Wasp - Cleptoparasite
Characteristics: Several different sapygid species are associated with solitary bees, so their appearance will vary, but adults are typically black and yellow and measure up to about 1/2 inch long (12.7 millimeters).
Sapygid wasps are cleptoparasites of both mason and leafcutter bees. The female oviposits her eggs into the nests of solitary bees, and the developing wasp larvae consume both the developing bee and the pollen loaf. These wasps then spin cocoons and overwinter undetected as adults alongside neighboring bees. Watch for Sapygid wasps in the summer! Sapygid wasps lay their eggs in the nests of bees while the female bee is away foraging.
What You Can Do: Watch for Sapygid wasps in the spring and summer! Sapygid wasps lay their eggs in the nests of bees while the female bee is away foraging. If you find this parasitic wasp hovering near your bee house, spray it with a fine mist of water to stun and then kill it.
Chrysidid Wasp - Body Snatcher
Characteristics: About 1⁄2 inch in length (12.7 millimeters) and are typically metallic green in color.
Multiple species of Chrysidid wasps also prey upon mason and leafcutter bees. These native wasps are not as destructive as Chalid wasps. Female wasps lay their eggs in nesting cavities while female bees are out foraging. Once the eggs hatch, the wasp larva attaches itself to the bee larva, which it begins to consume. After feeding, the wasp larva then spins a thin, semi-transparent cocoon and overwinters as adults. Unlike Chalid wasps, Chrysidid wasps only produce one generation per year.
What You Can Do: These are minor native predators and often don't require control. You can watch for Chrysidid wasps in the spring and summer to determine if you have a problem. Their metallic color makes them easy to spot. If you spot a lot of these wasps hovering near your bee house, you can spray the wasp with a fine mist of water to stun and then kill it.