Ants

• What You See: Lacking wings, a line of ants walk to the nesting holes by crossing the surface the bee house is mounted upon, such as a fence post, wall, or tree.
• Effect on Bees: An ant colony may be attracted to the sweet smell of pollen and nectar, bee cocoons, or developing larvae.
• What You Can Do: Ants can crawl across double-sided tape, try a stickier product like Tanglefoot or a layer of Vaseline spread along the back of the surface where the bee house is mounted. For a non-toxic solution that does not kill the ants, try our Ant Cant kit, which creates a slippery barrier that ants can't walk across.

Birds

• What You See: Nesting holes are strewn on the ground, birds are perching on the edge of the bee house, or you find a bird nest on top of your nesting holes.
• Effect on Bees: Nesting birds are attracted to large empty spaces in the bee house. Foraging birds want to eat loose cocoons or peck at filled nesting holes.
• What You Can Do: Install bird wire or hardwire cloth with 3/4" openings and loosely create a 3" bubble around the front of the bee house. Do not install the wire flush against the nesting materials because this keeps bees from being able to get in, too. Fill the empty space above the nesting holes or in the attic of your bee house with twigs or crumbled paper to deter birds from nesting.

Bears

• What You See: Nesting trays are on the ground and broken apart, the bee house is on the ground and may be broken
• Effect on Bees: Bears are attracted to the sweet smell of pollen, nectar, and bee larvae. Bears can destroy bee houses and take apart the wood nesting trays.
• What You Can Do: Move nesting houses out of the bear’s reach, above 8ft high.

Rodents: Rats, Mice, or Squirrels

• What You See: Rodents chew apart or leave nibble marks on cardboard BeeTubes and natural reeds. You may find loose nesting holes on the ground.
• Effect on Bees: Rodents are interested in eating developing larvae inside the nesting holes.
• What You Can Do: When nesting activity is complete, remove nesting holes from the bee house and place capped ends facing up in a chew-proof container made of thick plastic or metal (add a few air holes to the container).
• Product Recommendation: Upgrade to reusable wood trays

Raccoons

• What You See: Wood trays are torn apart or loose nesting holes are on the ground.
• Effect on Bees: Raccoons want to eat larvae or adult bees.
• What You Can Do: Install the bee house 6’ off the ground.

Earwigs

• What You See: Earwigs are skinny insects with pincers on their abdomens. You can find them inside of nesting holes.
• Effect on Bees: Earwigs are scavengers that are attracted to pollen, eggs, and developing larvae and they can’t penetrate mud walls. Earwigs are commonly found during bee nesting season and in the fall mason bee cocoon harvest.
• What You Can Do: Loosely roll up newspaper, bind it with a rubber band or string, dampen it and place this moisture trap inside the bee house. Dispose of the newspaper and earwigs in your compost pile. Another solution is to build a moat described in the ant section above.

Hornet or Paper Wasps

• What You See: You may see the beginning of a paper nest, which looks like an upside-down cup.
• Social wasps are not attracted to nesting holes. Wasps that build nests inside of nesting holes are solitary hole-nesting beneficial wasps who are preying on your garden pests.
• Effect on Bees: A social hornet or paper wasp queen decides to nest inside the empty space in your bee house.
• What You Can Do: Pesticides and chemicals will kill or deter your nesting bees and should be avoided. Wear protective clothing and spray the social wasp nest with high pressure water from a hose. Remove the nesting holes from the bee house or protect from the spray with a piece of cardboard. The best time to spray the social nest is in the late evening. Once removed, add twigs, rocks, or wadded paper to the empty space in the bee house to deter future social wasps. Another option is to let the nest run its course for the season because social wasps build a new nest every year.
• Pro Tip: You can also deter social wasps from building nests by installing a fake wasp nest. Inflate a paper bag, cinch the end closed, and hang the paper bag under the eave of your house. Social wasps are territorial and do not want to build nests near each other.

Parasitic Wasp: Monodontomerus (also known as mono)

• What It Is: Also known as mono, monodontomerus is a gnat-sized (3/16" or 4mm) parasitic wasp.
• What You See: Small, black, and with a long ovipositor (egg-layer), they hover and fly in a zig-zag pattern at nesting holes. Evidence of mono wasps are small holes in the sides of paper nesting holes where the adult mono wasps emerged. When harvesting cocoons, you may find a small hole in the side of an empty cocoon.
• Effect on Bees: Female mono wasps lay its eggs within developing bee larvae by inserting their flexible ovipositor through cracks in mud, thin walls of paper nesting tubes, or other weak spots in nesting materials. The infected mason bee larva lives long enough to spin its cocoon and the parasitic wasps are now encased in what appears to be a healthy cocoon. The sneaky wasp’s development time is short and they emerge as adults from the mason bee cocoons by chewing a small hole in the side.
• What You Can Do: Mason bee cocoons that did not emerge within a few weeks of release may be full of mono wasps and should be thrown away. Removing and protecting filled mason bee nesting materials removes the nesting holes while mono wasps are active. Check the BeeGuard Bag a week after removal from the bee house and you can easily kill parasitic wasps trapped inside of the bag.
• Pro Tip: If you suspect mono within a cocoon you can candle the cocoons. With a strong flashlight, make a pinhole in a piece of cardboard, place over the flashlight, and hold the cocoon over the pinhole. Mono larvae look like a mass of small bodies and a mono-filled cocoon can also look much brighter or red in color under the light. An adult mason bee is large and dark in color within their cocoons.
• Product Recommendations: In the late spring when female bees are done nesting, remove and protect filled nesting holes over the summer and store in a BeeGuard Bag.

Parasitic Fly: Cacoxenus indagator, Houdini Fly

• What It Is: A well-known pest in Europe, these small flies are members of the fruit fly family who are active when mason bees emerge in the spring. Named after their ability to escape, the young flies inflate their heads to break out of mason bee mud walls.
• What You See: Small gray flies with red eyes.
• Effect on Bees: Within a mason bee nesting hole the maggots eat the pollen loaf starving the mason bee larva. The maggots overwinter in the nesting holes and emerge as adults in spring. Adults sit outside the nest and wait to lay eggs in freshly built mason bee nests.
• What You Can Do: Harvest all mason bee nesting holes before spring and remove and crush any found maggots. If you cannot open your bamboo tubes or drilled blocks of wood, place the entire house and/or nesting holes in a BeeGuard Bag. Close the bag tightly and release the emerged bees daily in the spring. Crush any emerged fly to control this pest.
• For more detailed information on this emerging pest, please visit here.

Parasitic Wasp: Sapyga spp. (Sapygid Wasps)

• What It Is: Female sapygid wasps are fairly large wasps (about 1/3” long) and with their black and yellow bodies they look very similar to the well known social wasp, paper wasp, or hornet. There are a few different species of sapygid wasps and they may have white or yellow spots or a maroon band.
• Effect on Bees: The female sapygid wasp finds a recently laid mason bee nest and inserts her egg layer into the mud cap, laying an egg or two near the bee egg. Sapygid eggs hatch within 1-2 days and consume any other sapygid larva and the bee egg. The wasp larva eats the pollen loaf, spins a cocoon, and overwinters along with the neighboring bees. They emerge about the same time as the mason bee cocoons.
• What You Can Do: If you find this large parasitic wasp hovering near your bee nesting holes, spray it with a fine mist of water to stun and then kill it.

Pollen Mites

• What It Is: Pollen mites are the common name for Krombein's hairy-footed mites and are almost microscopic in size - you need a magnifier to see them. Pollen mites eat pollen, are picked up on flowers, and are found throughout North America and are more common in moist environments.
• What You See: Clear in color, what you actually see is a yellow or orange mass of mite feces. The mass of pollen mites and their feces can completely fill a nesting chamber and they are loose to the touch.
• Effect on Bees: Within a mason bee nesting hole the mites eat the pollen loaf and the mason bee larva can starve. The mites overwinter in the nesting holes and healthy adult bees spread the mites when they walk through unopened and infected nesting chambers in the following spring.
• What You Can Do: Do not reuse nesting holes because the pollen mites can easily spread. As you harvest mason bee cocoons in the fall, keep an eye out for signs of pollen mites. Use a dry brush to clean reusable wood trays to remove debris and pollen mites. Harvesting mason bee cocoons is the easiest and best way to reduce pollen mite infections.

Chalkbrood

• What It Is: A deadly fungal infection that is picked up on flowers.
• What You See: Chalkbrood cadavers are chalky, resemble the letter C, and the outer layer of chalkbrood breaks apart easily. Chalkbrood can range in color from salmon, brown, gray, or charcoal in color. Chalkbrood leaves behind a streak of fine black chalky powder.
• Effect on Bees: When ingested by a bee larva, the chalkbrood spore kills the larva and the larva becomes a chalkbrood cadaver that is a mass of chalkbrood spores. Healthy mason bees emerging from unopened nesting holes brush past infected chambers and spread the spores to your mason bee house and flowers. Without harvesting or providing fresh nesting holes, two or three years of this cycle can devastate your entire mason bee population.
• What You Can Do: Harvest your mason bee cocoons in the fall by opening nesting holes and dispose of all chalkbrood cadavers, being careful that other cocoons don't touch the chalkbrood. We recommend that you wash mason bee cocoons with cold water and a mild bleach solution, rinse with water, and pat them dry.
• Product Recommendation: Spray Clean Bee (a safe bleach alternative) on harvested mason bee cocoons that have been washed and dried. Apply Clean Bee to both sides of reusable wood trays.

Carpet Beetles

• What You See: Carpet beetle larvae are small, hairy and look like short fat caterpillars.
• Effect on Bees: The carpet beetle larvae eat mason bee cocoons. Mud capped ends or mud walls do not keep carpet beetles out of nesting chambers.
• What You Can Do: After female mason bees are finished nesting, remove nesting materials and store upright in a BeeGuard Bag. Store over the summer in a shed or garage with outdoor temperatures. During harvest eliminate these hairy pests.
• Product Recommendation: Remove and protect filled nesting materials over the summer in a BeeGuard Bag.

Ptinus Beetle

• What It Is: A small beetle known around the world to attack food and even museum items.
• What You See: The beetle larvae are short, fat and surrounded by thin, curly orange frass.
• Effect on Bees: The ptinus beetle eats the pollen loaf, mason bee eggs and larvae, and mason bee cocoons.
• What You Can Do: During mason bee cocoon harvest, remove all larvae of this pest.

Meal Moths

• What It Is: Meal moths are small silver or tan moths and they are also known by many names such as Indian meal moth, corn meal moth, flour moth, or grain moth.
• What You See: They are most damaging as pink or white hairless caterpillars (skinny, under an inch long, and actively wiggling during mason bee harvest) found within nesting holes. The larvae can also be found within thin, nearly clear cocoons.
• Effect on Bees: Meal moth larvae eat mason bee cocoons and they are not deterred by mud capped ends or mud walls.
• What You Can Do: After female mason bees are finished nesting, remove nesting materials and store upright in a BeeGuard Bag. Store over the summer in a shed or garage with outdoor temperatures. During harvest eliminate these pests.
• Product Recommendation: Remove filled nesting holes and store in a BeeGuard Bag.