Leaf cutter bees (Megachile) are solitary insects and important pollinators, but they become a nuisance when they target ornamental plants. Unlike honeybees, they do not live in large colonies; they work alone to build individual nests. Their activity is non-aggressive and poses no threat to human safety. However, the damage they cause to foliage often prompts gardeners to seek management strategies that protect plants without harming these beneficial insects.
Identifying Leaf Cutter Bees and Assessing Damage
Leaf cutter bees are typically small, ranging from one-fifth of an inch to one inch in length, sometimes resembling small honey bees. A defining physical feature is the scopa, a patch of dense hair on the underside of the female’s abdomen, used to transport pollen. This ventral pollen-carrying method distinguishes them from honeybees, which carry pollen on their hind legs.
The clearest sign of their presence is the characteristic damage they inflict on plants: clean, semi-circular or oval-shaped cuts along the edges of leaves. These precise cuts are harvested to line the brood cells within their nests. Preferred plant species often include roses, lilac, and ash, particularly those with softer leaves. While the appearance can be alarming, this leaf removal is primarily aesthetic and rarely causes significant harm or death to a healthy, established plant.
Non-Lethal Strategies for Protecting Plants
Protecting valuable foliage requires physical exclusion or topical deterrents to make the leaf surface unappealing.
One effective method involves covering susceptible plants with a fine mesh material, such as cheesecloth or lightweight netting. This physical barrier prevents the female bee from accessing leaves for nesting material while still allowing sunlight and water to reach the plant. The netting should be secured loosely around the plant to accommodate growth and ensure the bee cannot slip underneath.
Topical deterrents are another non-lethal approach that discourages bees from landing on the leaves. Strong-smelling substances, such as diluted garlic sprays or commercial repellents, can be sprayed directly onto the foliage. These treatments must be reapplied periodically, especially after rain, to maintain effectiveness during the bee’s active season, which typically runs from late spring through summer.
Managing and Discouraging Nesting Activity
Leaf cutter bees rely on pre-existing cavities to build their nests, provisioning them with cut leaf pieces, pollen, and nectar. Females search for holes in soft, rotting wood, the pith of thick plant stems, or other appropriately sized crevices. To discourage nesting near a home or garden, eliminate potential breeding sites by sealing exposed holes in fascia boards, window frames, or untreated wood with putty or caulk. Old, hollow reeds, bamboo stakes, or other debris that could serve as ready-made tunnels should also be removed.
If the bees are nesting in the cut ends of rose canes or other pithy plants, sealing these openings with white glue, sealing wax, or a thumb tack can prevent tunneling. Alternatively, providing designated nesting habitats away from prize plants can redirect their activity. Installing a specialized bee hotel or a cluster of pre-drilled wooden blocks offers a preferable, intentional nesting location. This strategy supports the beneficial pollinator population while moving the leaf-cutting activity to a less noticeable area.
When to Employ Professional or Chemical Removal
Chemical control is generally not recommended for leaf cutter bees because they are beneficial pollinators and solitary insects. Applying broad-spectrum insecticides to foliage is ineffective for preventing leaf cutting and poses a high risk to all beneficial insects. Since the female bee only lands briefly to make a clean cut and does not ingest the leaf material, topical chemical treatments are pointless.
Professional intervention is typically reserved for rare circumstances where the bees are causing structural damage or nesting in an inaccessible location inside a dwelling. If a large population is nesting within the internal walls of a home, a licensed pest control professional may be necessary to safely remove the bees and seal the entry points. Any chemical application, such as a contact-kill insecticide, must be highly localized and performed by an expert to ensure minimal impact on the surrounding environment.