The leafcutter bee belongs to the Megachile family of bees, and is another useful friend to gardeners as it provides a valuable and efficient pollination service for plants.
But they are also a very helpful friend to farmers. In fact, the US Agricultural Research Service says that 1 alfalfa leafcutter bee can do the job of 20 honey bees! (Ref 1)
Surprisingly, in research, they discovered that about 150 of these little bees working in greenhouses (or similar) can provide the pollination service of 3,000 honeybees!
Like mason bees, they are ‘cavity nesting’. This means they like to make their nests in ready-made cavities or in soft rotting wood that can be ‘excavated’. Once a suitable spot has been found, they will build cells using the pieces of leaf as lining, by overlapping segments of leaf to make a cylindrical cavity that looks a little like a cigar. Each cell is sealed up with a little segment of leaf. In parts of Europe, some species line their egg cells with petals instead of leaves. Nests are small: only around 4 to 8 inches long.
Below is a small amount of video I managed to capture, of a leafcutter bee female carrying a segment of leaf back to her nest. It's a very short clip, because having positioned the solitary bee house, I then proceeded to put heavy pots and plants in the way, making it difficult for me to sustain filming for a long period of time, so that most of my video clips were very shaky and not at all very good!
But anyway, the segment of leaf is grasped and carried below the body of the bee, and transported to the nest.
Note, Leafcutters always cut away segments of leaf in a very neat fashion. Jagged cuts or rips in leaves are nothing to do with leafcutter bees (see the image below).
The newly emerged females begin constructing nests after they emerge in Spring. In each cell they will lay a single egg, and supply it with pollen upon which the larva can feed once it hatches. The larvae pupate and develop inside these cells. They will over-winter in their cells as mature larvae, and emerge as adults the following spring or early summer.
How Do They Differ From Honey Bees?
On first sighting, many species of solitary bees can easily be mistaken for honey bees or even hoverflies. So how can you tell the difference between honey bees and leafcutters, if the leafcutter is not engaged in the activity of cutting leaves or building its nest, but instead, is foraging on flowers?
One give away lies in their methods for collecting pollen. Worker honey bees, like bumblebees, collect pollen in their pollen baskets or ‘corbicula’ on the hind legs, then transport it back to the hive or nest.
bees do not have pollen baskets on their hind legs. Instead, they
collect pollen on hairs on the underside of their abdomens. When the bee is carrying pollen, it is quite visible as a pale yellow colour. See the photograph below.
The photograph above of Megachile centuncularis was taken in my garden. This leafcutter is foraging on a particular variety of low growing bedding campanula.
Have you ever noticed neat little segments cut away from roses, lilac or other shrubs?
If it’s leafcutter bees, there will be a crescent or almost circular shaped hole in the leaf. If you should find this, do not worry, usually it will not harm your plants, although rarely, you could see a fair amount of damage, but this is not the norm. Plants can usually can shake off a little damage. (Remember, plants survive pruning and dead–heading!).
So, please don't spray your plants with pesticides!
How To Attract Them
It’s possible to encourage them into your garden by providing bundles of hollow canes, or a log of wood drilled with holes around 1cm in diameter (don’t use varnish, preservatives or any other chemicals). If the holes in the canes of the log are too small, then your ‘bug house’ is more likely to be occupied by ladybugs or some other insects.
I have had great success with a bug house sited against a sunny fence. This year, I decided to make further provision for them in my garden, this time with hollow canes, again with great success. Attracting leafcutter bees to the garden is very rewarding. They are fascinating to watch, and in a way, amusing: to see a little bee carrying a piece of leaf as large as itself, or even larger, is wonderful to see!
Ref 1: http://www.ars.usda.gov/is/pr/1997/970820.htm
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