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The Broad-Handed Leafcutting Bee

Kim Fellows 

Last summer, I noticed a native bee that I had previously never observed in Kitchener, ON. I first noted the fuzzy bee on Stachys byzantina, the soft-to-the-touch plant also known as lamb’s-ear, and then observed it foraging on hairy mountain mint, Pycnanthemum verticillatum, in the pollinator fedge around the Hope and Unity Community Garden. A closer look told me that it was a male specimen, likely Megachile latimanus.

The word latimanus means “broad-handed,” and refers to the foreleg of the male, which is fringed heavily with a comb of hairs. Knowing that male bees typically do little but contribute their genetic material to the next generation, I surmised that the eye-catching fringe would serve to attract females. However, Cory Sheffield, a bee expert and curator at the Royal Saskatchewan Museum, shared: "I do not think the legs function for attraction, as not all Megachile have these modifications. My understanding is that there are glands within the concave surface which the males cover the face of the female with (the secretions thus detected by the antennae of the female). So it may serve a role in reproduction. Some of the crabronid wasps have males with beautifully patterned front legs too."

Megachile bees are also known as leafcutting bees, as they cut and use pieces of leaves as their main nesting material. Leafcutting bees tend to favour the leaves of rose, lilac, green ash and Virginia creeper, but in a pinch, will also use other varieties. Generally, their trimming does not harm the plants. These native leafcutting bees are solitary, meaning they do not nest in colonies. Each female prepares her own nest, usually tunneled out of partially rotted wood or made in the pith of canes and hollow-stemmed weeds, or, as is the case with this particular species, soil is used as a nesting substrate.

The bees use the leaf fragments to line their nest cells. Leafcutting bees work quickly, typically making a smooth semi-circular cut about 3/4-inch diameter from the edge of the leaf, in 10 seconds or less. The resulting leaf-lined cell is then packed with a "loaf of bee bread" – a ball of pollen and nectar – and an egg is laid on the “loaf." The hard working bees then seal the cell with more plant material, and move on to building another cell. In larger nests, they may create a dozen or more such cells one after the other.

The pupae overwinter in the nest, emerging as adult bees the following spring. One generation is produced per year, and their leaf-cutting activities typically reach their peak in late June and July.

So from now on, if you see little holes cut into your leaves on some garden plants, you can consider yourself very lucky, knowing that pollinators are hard at work in your garden.

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Kim Fellows is the Coordinator of Pollination Canada.

 

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