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More About Leafcutter Bees

Because Rebecca had a question about the leafcutter bees in my last post, I thought I would expand a bit on their biology.

Leafcutter bees (genus Megachile) are solitary bees that are important pollinators. As with most solitary bees, each female constructs its own nest.

The leafcutter bees prefer to nest in pre-formed holes about the size of a pencil (roughly) in diameter. They often nest in wood or hollow stems, although they will also use sites like holes between bricks or even screw holes in patio furniture.

The female bees cut circular patches out of leaves with their mandibles.

They then carry the pieces back to the nest hole they chose and use the leaves to line the cavity and construct chambers to lay their eggs in.

Below is a completed nest that I found between two cement blocks:

Inside this bundle will be several chambers separated by neat walls of leaf. Within each chamber will be a ball of bee bread, a mixture of nectar and pollen (see sweat bee post for what this looks like). On the ball will be a single white egg, which will hatch into a larva and consume the bee bread. It will pupate within the chamber and later emerge as an adult.

Leafcutter bees harvest leaves from relatively few species of plants. In addition to the pomegranate, they will also use the bracts of bougainvillea, creating a lovely bright pink or red nest. The plants they seem to prefer most are roses, which gets them into trouble with rosarians.

As with many solitary bees, leafcutters are important pollinators. The females carry the pollen in the bristly hairs on the underside of their abdomen, which are called scopae.

It is the white area on the underside of the abdomen in this photograph.

Leafcutter bees are managed commercially for pollination of alfalfa for seed production. The idea is that honey bees avoid the elaborate tripping mechanism of the alfalfa flower, but the leafcutter will readily use and pollinate the flowers. The alfalfa leafcutter bee is an introduced species.

The farm were I worked once brought in leafcutters to pollinate an alfalfa crop. Although they are solitary, these leafcutters will nest in aggregations. The farmer brought in a smallish trailer piled high with leafcutter nests, each with an active female. During the day there was a cloud of bees flying to and from the trailer. It was actually very cool, and I wish I had taken a few pictures.

Have you ever seen leafcutters in action?

Places to find out more about solitary bees:

18 comments to More About Leafcutter Bees

  • Roberta,

    I’m teaching backyard gardeners to raise native and solitary bees. These photos that you have here are amazing. May I have your permission to use them if I credit you and your website?

    Dave

  • Maggie

    Thanks for this. I found a beautifully crafted chamber while digging in my garden. Since it was damaged anyway, I peeled off the layers and was amazed at the symmetry and construction. It took me a long time to find out what it was. Wish I’d taken pictures.

  • Roberta

    Ah, yes, since it was damaged anyway it would have been great to have photographs. Glad this helped you figure out what it was.

  • [...] bees is about 300′ (12om) from their nest. In this series of photos by Roberta Gibson on her blog about leaf cutters, it is interesting to watch the leafcutter in action cutting a nice circle out of this leaf for her [...]

  • Anna Hales

    A leafcutter has just finished building a ‘nest’ in our new bee house; how long does it take for the new bee to emerge?

  • joan sessions

    i recently found a wonderful, intact chamber that i suspected was made by a leafcuttr. I have tons of bees around. was so cool to find, i put it back where i think it belonged and i think the owners came back. Bees really need our help so please please no pesticides!!!!!!

  • Roberta

    When it might emerge depends on a number of things such as temperature and location. Right now ours are likely to stay in the nest until next spring.

  • Tina

    I think I have a leaf cutter nesting in an old herb garden wall hanging container. I didn’t know they existed until I did some googling! It is regularly flying into one of several holes in soil with sections of leaves, when I googled them it said they were active early spring, do you think it may be down to the weird weather this year or is it usual for one to be nesting now? I am aware these bees are in decline so will not destroy her nest – would it be ok to move the container though?

  • Roberta

    I would be careful to keep the container under similar conditions, that is don’t move it into direct sunlight if it in the shade right now. Otherwise it should be fine.

  • Mira

    I couldn’t figure out what was cutting off tme ends of my Morning Glory’s
    Leafcutter Bees!

  • maggie

    Siting on my garden bench and noticed a bee flying underneath it. Looked and saw the bee crawling inside the screw holes. Next morning noticed debris underneath the same spot on the floor. Saw that they were bits of leaf; circular in shape. Next day all debris gone and two screw holes nicely packed with the same bits of leaves and this all in early September. The bees actually worried us away from sitting on the bench whilst this was ongoing by divebombing us !

  • Roberta

    Maggie,

    Thank you for sharing your observations. I’ll bet all is quiet now.

  • Maddie

    i love your RESEARCH. i’m going to share lots of imformation with my science olympiad class and this is just PERFECT RESEARCH!

  • [...] this series of photos by Roberta Gibson from her blog about leaf cutters, it is interesting to watch the leafcutter in action cutting a nice circle out of this leaf for her [...]

  • Meg T

    Yesterday watched a leaf cutter bee bringing back pieces of leaf which it took down into the side of a flower pot holding a fuchsia and soil covered with bark mulch. Might this stunt the growth of the plant? It is smaller than another fuchsia in a similar pot with same soil.

    The pot has previously, weeks prior to noticing the bee, been treated with ant powder and vine weevil solution. Will these endanger the grubs?

  • Meg T

    Are they all females?

  • Roberta

    Meg,

    When the female leafcutter bee makes a nest, it is about the width of a pencil and roughly two inches long. It will not interfere with the fuchsia plant at all. The nest is made up of leaves and pollen for food, with bee grubs inside. We often have leafcutter bees share flower pots, and frankly it is usually tougher on the bees (when the plant is watered) than it is on the plant.

    As for the pesticides, we can hope that the leaves around the nest will provide a protective layer for the grubs. If anything, it probably effected the mother bee more than her offspring.

  • Roberta

    Meg,

    Regarding your question about whether they are all females: the females work hard to make the nests and provide for the offspring, so they are the insects you see most often. There are male leafcutter bees, too, but you don’t see them as much. Here are some photographs of male leafcutters – http://blog.wildaboutants.com/2012/09/19/wordless-wednesday-male-leafcutter-bee/

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