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Megachile


Photo by Hartmut Wisch
Megachile – large leaf-cutter bees (family Megachilidae)
by Lisa Schonberg and Mace Vaughan (Xerces Society) and Gretchen LeBuhn (SFSU)

Genus summary: Megachile is a large genus that occurs worldwide. There are over 1500 species in the world, 139 in the U.S. and Canada (Michener 1994), and about 21 in New York State (Danforth & Magnacca 2002). They are commonly known as leaf cutter bees because they cut the leaves or flowers of plants and use the pieces to form nest cells. They are the “large leaf-cutter bees,” whereas the genus Osmia are the “small leaf-cutter bees.”

Floral relationships: Megachile includes both specialist and generalist foragers. Some species specialize on flowers of plants from the family Asteraceae. Megachile rotundata, the alfalfa leafcutter bee, is one of the most important agricultural pollinators. It is an introduced species used commercially to pollinate alfalfa (Delaplane & Mayer 2000).

Nesting habits: Megachile are primarily cavity nesters and nest in a wide variety of habitats and sites, but they all line their brood cells with leaves or petals of plants. Many species are opportunists; their nests have been found in a variety of man-made structures such as garden hoses and crevices in walls. These species prefer to nest in soft rotted wood, abandoned beetle tunnels and hollow plant stems of large pithy plants (i.e., rose canes, green ash, lilac, Virginia creeper). Other Megachile spp. use resin and mud to build above-ground nests , and a few species nest in the ground (O’Toole & Raw 1999). Many people believe that Megachile nesting habits are harmful to plants, even though their leaf-cutting and stem-nesting activities cause little damage. Some farmers take the unnecessary precaution of covering plants with cheesecloth when Megachile are active .

Diagnostic characteristics: There is wide variety in form and structure among Megachile spp. Megachile are medium to large bees, 0.4 to 0.8 inches long. The genus includes the largest bee in the world – a Malaysian species with a 2.5 inch wingspan. Many Megachile are smoky colored and stout-bodied, with a flattened abdomen with pale hair bands. Megachile females carry dry pollen on scopa (brushes of hairs) on the underside of their abdomen rather than on their hind legs like most bees (O’Toole & Raw 1999). This is characteristic of all females in the family Megachilidae, which also includes Anthidium, Osmia, and Hoplitis. Females of this group often have huge mandibles for cutting leaves . They have a pugnacious look to their abdomen as they strut about on flowers.

Similar taxa:
Known conservation concerns:

Interesting fact: It only takes two or three seconds for Megachile to cut a piece of leaf. Just before she finishes cutting the leaf,a female Megachile starts to beat her wings so that she is already flying by the time the leaf fragment is severed from the plant. In many Megachile spp., the female flies off with the leaf while gripping its edges and holding it close to her body; she then lands briefly to get a better grip on the piece of leaf, pulling it forward and grasping it between her mandibles and first two pairs of legs (O’Toole & Raw 1999).

Additional resources:

Key to Eastern Megachile females at Discover Life
Key to Eastern Megachile males at Discover Life

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