Solitary Bees
Mono Wasps | Sapygid Wasps | Pteromalus Wasps | Pollen Mites | Chalkbrood | Houdini Fly Maggots
Ants | Beetles | Birds | Earwigs | Hornets | Meal Moths | Larger Pests
Parasites, Pests, and Predators
This list may seem like a lot, but most of these problems can be managed using the same few easy methods.
- Use strong, clean nesting materials.
- Protect stored nesting materials in a fine-mesh bag.
- Harvest cocoons.
- If you see a parasite, squish it!
Parasitic Wasps
Monodontomerus Wasps: Small (~4mm), black wasp with a long ovipositor. The adults fly in a zig-zag pattern at nesting holes. Their long, flexible ovipositor easily penetrates paper, mud, or other weak spots in nesting tubes to deposit eggs into a developing bee larva. The mason bee larva lives long enough to make its cocoon, then the wasps within feed on the larva and emerge from the cocoon when they’re finished. Tiny holes in the sides of paper nesting tubes or a small hole in the side of an empty mason bee cocoon during cocoon harvesting are signs of mono. Choose thick cardboard, natural reeds, or reusable wooden trays. Discard mason bee cocoons that do not emerge within a few weeks of release, as they may be full of mono wasps. Store nesting materials in a fine-mesh bag to help keep them out. If you see one that has hatched INSIDE your mesh bag, squish it!
Sapygid Wasps: Larger (~8-9mm) black and yellow wasps, similar looking to a paper wasp. Adults find a newly constructed mason bee nest and pierce the mud cap, laying an egg near the bee egg. The wasp egg hatches quickly and eats the bee egg and pollen loaf. Then it spins its own cocoon and overwinters in the nesting tube, emerging as an adult in the spring. If you see a sapygid wasp near your bee nesting holes, spray it with a fine mist of water to disable it and then kill it.
Pteromalus Wasps: Tiny (~2-3mm) black wasps. Adults lay eggs within leafcutter bee eggs and overwinter in the leafcutter bee cocoons. They emerge before leafcutter bees and go on to lay eggs in the remaining incubating cocoons. You may see tiny exit holes in your leafcutter bee cocoons. If you see a pteromalus wasp near your bee nesting holes, spray it with a fine mist of water to disable it and then kill it. Store nesting materials in a fine-mesh bag during incubation. Pteromalus usually emerge about 9-12 days after incubation begins. If you see one in your mesh bag, squish it!
Mites, Fungi, and Flies
Pollen Mites: Microscopic thieves that feed on your bee’s pollen loaf, potentially causing your bee to starve. Bees can pick up pollen mites from flowers while foraging and then unknowingly deposit them in their offspring’s pollen loaf. The mites can migrate into neighboring chambers or the bees may spread them as they emerge and crawl through the nesting tube. Emerged adults then carry the mites to new flowers. The best defense is harvesting your cocoons so that adults don’t walk through and spread mites.
Chalkbrood: A fatal fungal infection that bees pick up while foraging on flowers. The infection kills the larva and turns it into a mass of spores. As nearby healthy bees emerge, they spread the spores to new flowers and other nesting holes. The best defense is harvesting your cocoons so that adults don’t walk through and spread spores.
Houdini Fly Maggots (NEW THREAT): Any emerging pest. This small, red-eyed and gray-bodied fly produced maggots that eat your bee’s pollen loaf, causing your bee to starve. They can quickly overrun an entire bee house. Storing nesting materials in a fine mesh bag can help keep them out. If you see a fly or maggot, squish it!
Other Pests
Ants: May be attracted to pollen loaves or the larvae themselves. Spread a layer of Vaseline along the back surface where the bee house is mounted.
Beetles: Keep carpet beetles and ptinus beetles out by storing nesting materials in a fine mesh bag. Dispose of any beetle larvae seen during cocoon harvesting.
Birds: You may see nesting holes on the ground or birds perching or nesting on your bee house. Fill open spaces with twigs or crumpled paper to deter nesting. You can place chicken wire or hardware cloth with 3/4 inch openings around the front of the bee house. Leave at least 3 inches between the nesting tube opening and the wire, creating a “bubble.” If the wire is flush with the nesting tube openings, the bees won’t be able to access the nests.
Earwigs: Earwigs scavenge on pollen, eggs, and larvae. Make a moisture trap by loosely rolling up newspaper, binding it with a rubber band, and placing it inside the bee house. Then dispose of the newspaper and earwigs in your compost pile.
Hornets or Paper Wasps: These wasps are not competing with your bees, so you could choose to leave them alone. If you do decide to remove their nest, do it in the late evening. Wear protective clothing and spray the wasp nest with high pressure water from a hose. Either remove the nesting holes from the bee house or protect them from the water with a piece of cardboard. After removal, fill the empty space with twigs or crumpled paper to deter wasp nesting.
Meal Moths: Adults are small, silver or tan moths. Caterpillars are pink or white. Store nesting materials in a fine mesh bag. Dispose of any moths or caterpillars seen during cocoon harvesting.
Larger Pests: Rats, mice, squirrels, raccoons, or bears may want to feed on the contents of your bee house. Be sure to install bee houses 5+ feet off the ground. Raise to 6-8 feet off the ground if necessary. If rodents want to chew on your nesting tubes while they are in storage, keep them in a thick plastic or metal container with air holes.
