Mortar bees are solitary bees that tunnel into the soft or crumbling mortar joints between bricks to lay their eggs. The most effective way to get rid of them is to repoint (replace) the damaged mortar they’re nesting in, which removes their habitat and prevents them from returning. Unlike a wasp nest you can knock down, mortar bee activity is tied to the condition of your masonry, so the real fix is a repair job, not a pesticide.
Why Mortar Bees Target Your Walls
Mortar bees, most commonly mason bees and similar solitary species, don’t eat mortar. They excavate it to create nesting tunnels where they deposit pollen, nectar, and a single egg in each cell, then seal it off with mud. They specifically seek out mortar that’s already soft, sandy, or deteriorating. Healthy, well-bonded mortar is too hard for them to dig through.
This means mortar bees are a symptom, not the root cause. If you see small, perfectly round holes (roughly the diameter of a pencil) in your mortar joints, the mortar was already failing. Older homes with traditional lime-based mortar are especially vulnerable because lime mortar is softer than modern cement-based mixes. The bees simply accelerate damage that was already underway.
When They’re Active
Mortar bees typically emerge in early spring and stay active for roughly six to eight weeks, usually from mid-April through mid-June, coinciding with fruit tree blossoms. After mating, males die quickly while females spend their remaining weeks nesting. The adult stage you actually see lasts only about three to six weeks, even though the full lifecycle spans a year. The rest of that time, developing bees are sealed inside their cells as larvae and pupae.
This short active window matters for two reasons. First, it tells you when to expect them. Second, it tells you when to schedule repairs. The best time to repoint mortar is after the bees have finished nesting in late summer or early fall, when the cells are sealed and you won’t encounter active adults. Repointing in winter or early spring, before emergence, also works well.
Repointing: The Permanent Fix
Repointing means removing the old, damaged mortar and filling the joints with fresh mortar. It’s the only long-term solution because it eliminates the soft material the bees need to nest in. Filling individual holes with caulk or expanding foam is a common shortcut, but it traps moisture, looks bad, and doesn’t address the surrounding mortar that’s also deteriorating. The bees will simply drill new holes nearby.
For a proper repoint, old mortar should be removed to a minimum depth of two to two-and-a-half times the width of the joint. For most brick walls, that means removing mortar to a depth of about half an inch to one inch. This ensures the new mortar bonds securely and won’t pop out. You can use a cold chisel and hammer for small areas, or a mortar rake for larger sections. Avoid power tools like angle grinders on older brick, which is softer and chips easily.
Choosing the Right Mortar
Getting the mortar mix right is critical, especially on older homes. Traditional mortar was a simple blend of lime putty and local sand, typically one part lime to three parts sand. If your home was built before the mid-20th century, it likely has lime-based mortar, and you should match that softness. Using modern Portland cement mortar on old, soft brick can cause the brick itself to crack because the mortar is harder than the masonry it’s holding together.
Mortar is graded by strength. For older brick homes, a softer Type O or Type K mix is usually appropriate. Type O uses a ratio of 1 part cement to 2 parts lime to 9 parts sand. Type K is even softer at 1 part cement to 3 parts lime to 11 parts sand. For modern brick construction, a standard Type N mix (750 psi compressive strength) works for most residential walls. If you’re unsure, a mason can match the existing mortar by examining a sample.
Dampen the joints before applying new mortar so the brick doesn’t pull moisture out of the mix too quickly. Pack the mortar in firmly, building up in layers if the joint is deep, and tool the surface to match the surrounding profile. The repair should be nearly invisible when done well.
Deterrents While You Wait for Repairs
If repointing isn’t immediately possible, a few measures can reduce nesting activity during the spring season. Spraying water on active nesting areas in the morning can discourage females from starting new tunnels, since they prefer dry conditions for digging. Hanging fine mesh netting over the worst sections of wall creates a physical barrier, though it isn’t attractive and works better as a temporary measure.
Some homeowners apply a thin coat of masonry paint or sealant over damaged joints to harden the surface. This can deter bees in the short term, but it also traps moisture behind the seal, which can worsen deterioration over time. It’s a stopgap, not a substitute for repointing.
Why Pesticides Are a Poor Choice
Spraying insecticide into mortar bee holes kills individual bees but doesn’t solve the underlying problem. New bees will find the same soft mortar the following spring. You’re also killing pollinators that are genuinely beneficial. Mason bees are among the most efficient pollinators of fruit trees and garden crops, and solitary bees in general don’t sting aggressively. Females can sting but rarely do, since they have no colony to defend.
Pesticide residues in masonry can also leach out with rainwater, affecting nearby soil and plants. Oregon State University’s extension service specifically recommends avoiding harmful or unnecessary pesticide use around solitary bees, and encourages providing alternative nesting habitats instead. If you’d rather redirect the bees than eliminate them, a simple mason bee house (a block of wood with drilled holes, or bundled paper tubes) placed nearby gives them a preferable nesting option and keeps them away from your walls.
Assessing the Damage
A few scattered holes in otherwise solid mortar is a minor issue. The mortar around those holes is likely still sound, and a small patch repair handles it. But if you can scrape mortar out of the joints easily with a flathead screwdriver, or if you see widespread crumbling, the bee activity is a sign of broader mortar failure that needs systematic repointing across larger sections of the wall.
Left unrepaired, mortar bee tunnels allow water into the wall. Freeze-thaw cycles then crack the brick and erode the mortar further, creating more nesting sites the following year. What starts as a cosmetic nuisance can become a structural issue over several seasons. Catching it early, when damage is limited to a few joints, saves significant cost compared to a full wall repoint later.
For walls with extensive damage or historic brick, hiring a mason experienced with lime mortar is worth the investment. Incorrectly matched mortar can cause more damage than the bees did.