Leafcutter bees belong to the genus Megachile, a diverse group of solitary bees. The female works alone, constructing and provisioning her own nest without the help of a colony or queen. These insects are efficient pollinators of many wildflowers and commercial crops, including alfalfa and blueberries. Their common name comes from their unique habit of cutting precise, circular pieces of leaves or flower petals to build their nests.
Geographic Range
Leafcutter bees are one of the most widespread bee genera globally, with species found on every continent except Antarctica. This distribution includes North and South America, Europe, Asia, Africa, and Australia. The exact species present can vary significantly by region.
Their distribution is heavily influenced by the availability of flowering plants, which provide the nectar and pollen they need. For example, the Alfalfa Leafcutter Bee (Megachile rotundata), though native to Europe, is now managed globally for its role in pollinating alfalfa crops. This widespread presence underscores their adaptability to various climates, from arid deserts to temperate zones.
Specific Habitat Preferences
Leafcutter bees favor habitats that offer suitable nesting sites and a plentiful supply of pliable plant material. Within their expansive geographic range, they thrive in diverse environments, including temperate forests, scrublands, deserts, and grasslands. Their preference is driven by the presence of pre-existing cavities for nesting.
The bees are common in human-managed landscapes, such as agricultural fields and urban gardens. These areas provide ideal conditions, including flowering plants and readily available sources of soft, broad leaves, like those from roses or lilacs. Environmental factors like temperature and moisture are also important, but the presence of suitable nesting cavities is the primary determinant of a local population’s home range.
Nesting Habits and Construction
Nest Location
The leafcutter bee’s home is a pre-existing, tube-shaped cavity, as they do not excavate their own tunnels in solid material. Females seek out narrow, protective spaces such as hollow plant stems, the pithy centers of canes, abandoned tunnels made by wood-boring insects, or cracks in dead wood. The size of the cavity, often about the diameter of a pencil, can influence the sex of the developing offspring.
Cell Construction
Once a suitable tunnel is located, the female begins construction using her namesake material. She uses powerful mandibles to snip nearly perfect, semi-circular pieces from leaves or petals, often from plants like rose, lilac, or alfalfa. These pieces are carried back to the nesting site, held between her legs, to be used as building material for the brood cells.
Provisioning and Sealing
The bee starts at the deepest part of the tunnel, lining the cavity with leaf fragments to form a thimble-like structure. She then provisions this cell with a mixture of nectar and pollen, which is collected on a dense brush of hairs, called the scopa, located on the underside of her abdomen. This mixture, sometimes called a “bee loaf,” is the sole food source for the developing larva.
After the food supply is placed inside, the female lays a single egg on the provision, and then seals the cell’s opening with several circular pieces of leaf. She repeats this process, building a linear series of cells, one after another, until the tunnel is full, sometimes containing up to 20 individual cells. The final cell is capped with a thick plug of leaf material, and the female dies shortly after, leaving her offspring to develop and emerge the following season.