All-Season Pests and Predators of Cavity-Nesting Bees
Installing bee houses and hotels are great ways to encourage nesting, protect pollinators, and educate communities about bees' vital role in food production and ecosystem services. Unfortunately, productive bee nests are loaded with pollen, nectar, and bee larvae, making them a smorgasbord of food resources for pests and predators!
This article highlights common all-season pests and predators attracted to spring mason bees, summer leafcutter bees, and wild native bees. For more species-specific enemies, check out Parasites and Diseases of Mason Bees and Parasites and Diseases of Leafcutter Bees.
Ants & Earwigs
Ants and earwigs are an occasional nuisance to mason and leafcutter bees. Damage is usually restricted to newly laid, exposed bee eggs or loose cocoons in a hatchery. More common in the eastern US, earwigs will also scavenge on pollen provisions and leafy nest materials. Once females seal their nests with mud or leaves, the damage is usually minimal.
What You Will See: A line of ants walking to the nesting materials by using the bee house's mounting structure, like a fence post, wall, or tree, as a bridge. You will see earwigs crawling inside or around nesting materials.
What You Can Do: Since these pests usually gain access to nests by crawling up shelter legs, coat the base of the shelter with a sticky 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 AntCant, which creates a slippery barrier that ants and other crawling insects can't walk across. Make sure to remove any vegetation that is touching the shelter - it acts as a bridge for these insects.
The majority of spiders aren't interested in solitary bees or their nests and don't pose a threat. However, some jumping spiders and crab spiders are opportunistic and will attempt to feast on foraging adults if given a chance.
What You Will See: Spiders or spider webs inside or near your bee house.
What You Can Do: Managing spiders is tricky. There is little you can do to protect your adult bees from the spiders waiting on the flowers for a dinner guest to arrive. Of course, in this case, the dinner guest is dinner — the nature of predator-prey relationships. However, if you notice spiders are constantly hanging out at the opening of your nesting materials, there are a few things you can do:
- Remove any spiderwebs from inside or around your bee house. If you see spiders lurking on your bee house or nesting materials, watch them for a while, and if you notice they're attacking your bees, feel free to kill or move them to an area far away from your bee house.
- Since spiders usually gain access to nests by crawling up shelter legs, coat the base of the shelter with a sticky product like Tanglefoot or a layer of Vaseline spread along the back of the surface where the bee house is mounted.
- Make sure to remove any vegetation that is touching the shelter - it acts as a bridge for these insects.
Many species of birds will prey upon both adult and dormant bees. Starlings, robins, swallows, tanagers, and woodpeckers can cause significant damage to adult bees, bee larvae, and nesting materials. Once these predators recognize the bee nest as a food source, they are relentless.
What You Will See: Evidence includes finding nesting materials on the ground, birds perched on the edge of the bee house, or a bird's nest on top of or near your nesting materials.
What You Can Do: There is little you can do to protect your adult bees from birds once they leave the nest to mate and forage. It's a natural predator-prey relationship that has been around since the existence of animals. However, you can do a few things to protect the bees, larvae, and nesting materials inside your bee house.
Create a bubble on the front of your bee house with wire mesh to protect the shelter from intrusion. The size of the wire openings and the distance between the wire guard and the nesting materials are important to get right! Ideally, the gaps should be about 3/4," and the bubble should be a minimum of 1.5 to 2 inches and maximum 3 to 4 inches from the nesting materials. Openings smaller the 3/4" can damage bee wings. If the bubble is larger than 3 to 4 inches, it can deter bees from nesting. If the bubble is too short, birds with longer beaks and squirrels can reach the nesting materials.
Pro Tip: Bees can have trouble navigating in and out of wire mesh, so only use this method when necessary, not as a preventative measure.
Product Recommendation: Crown Bees sells a protective bird guard that fits securely on our cedar houses.
Rodents & Raccoons
Rodents such as chipmunks, mice, and squirrels will also take advantage of an easy meal of bee larva and dormant bees.
What You Will See: Rodents chew apart or leave nibble marks on Cardboard BeeTubes and Natural Reeds. You may find loose nesting holes on the ground.
What You Can Do: Secure nesting materials with wire mesh or a bird guard as necessary. You can also coat the bee house base with Vaseline or Tanglefoot, although this method may not be strong enough to stop larger rodents from reaching the nesting materials. Raccoons and rodents can reach loose nesting materials, like cardboard tubes and natural reeds, through the bird guard, so you may want to upgrade to wood blocks or create a bubble of wire mesh to prevent dexterous critters from removing your nesting materials.
When nesting activity is complete, remove nesting materials from the bee house and place capped ends facing up in a thick plastic or metal chew-proof container. Don't forget to add a few air holes to the container!
Hornets & Paper Wasps
Hornets and paper wasps are social insects, like honey bees. Adults feed on nectar and prey upon small insects to feed their offspring. They are often not a problem for mason and leafcutter bees unless they build their nests near or inside your bee house.
What You Will See: You may see the beginning of a paper nest, which looks like an upside-down cup.
Pro Tip: Social wasps are not attracted to nesting materials or the solitary bees inside the materials. If you see wasps building nests inside your nesting materials, they are solitary, beneficial wasps preying on garden pests. Like solitary bees, these wasps are not aggressive and only sting when threatened.
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 them 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 spaces 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.
Bears, Oh My!
We all know bears are notorious for eating honey and destroying beekeepers' honey bee hives. But, did you know that bears also have a taste for solitary bees; they are attracted to the smell of pollen, nectar, and developing larvae and can devour the entire nesting site in a short period.
What You Will See: Bears often break apart nesting materials and bee houses and get at the pollen and larvae. If you find broken pieces strewn all over the yard, it's likely a bear!
What You Can Do: If you live where bears are a concern, you should place the solitary bee house 8 - 10 feet off the ground. Most solitary bees don't forage higher than 10 feet, so only place your bee house up high if bears are an issue.
Honey Bees & Bumble Bees
Ever notice honey bees or bumble bees flying around the outside of your solitary bee house? We've had many bee raisers ask us if these social bees are predators of solitary bees. We are happy to report that they are not! They are likely attracted to the scent of nectar and pollen but will not invade a solitary bee nest to retrieve these food sources.
However, there is evidence that large populations of honey bees can pose a threat to solitary bees, not as a predator but as a competitor. There is evidence that introduced bees like honey bees can lead to solitary, native bee declines when they compete for the same nectar and pollen sources in gardens and native vegetation areas.