A simple construction built with metal cans and bamboo tubes has attracted several species of tube-nesting bees to my garden since I first tried it in 2011. They include leafcutter species which line their nest-cells and seal the ends with discs cut from leaves, laying an egg on the food store in each cell. The most frequent in my garden is also the biggest: The Wood-carving Leafcutter Bee, Megachile ligniseca, larger than a honeybee, though quite different in appearence.
Here is how I make them:
1. From a supermarket get fruit or soup cans of two widths, one of which will fit inside the other with a narrow space between their walls. The small one should be the same length, or a bit longer than the large one. Remove the tops and use the contents. Wash and dry the cans. After a season in the garden they will rust, but that doesn’t matter.
2. From a garden centre get several bamboo canes, not too narrow and not too wide. Choose sections with apertures from 9mm to 12mm. Using a saw, cut them into equal lengths, the length of the small can or slightly longer. Avoid the nodes – they should be open at both ends. Remove the pith with anything you can conveniently shove through, like shirt-hanger wire.
4. Find a fence post or wall in a sunny place facing SE to S. Drill a hole through the end of the larger can and fix it up with a screw, from 3 to 5 feet above the ground.
5. Fit the small can into the large one and wedge it in with pieces of split bamboo.
You are ready for the bees, though it may take a while – up to a year, even – for them to discover it. Once used successfully the tubes will be inhabited year after year. I have seen them do their own spring-cleaning in June.
In September or October when nest-building is finished, remove the inner can and store it in an unheated shed away from the rain. This will avoid damage to the bee cells from severe weather and small birds during the winter months. Remember to bring it out again in April the following year and put it back in place. The bees will emerge in early June
Some of the tubes may be used by mason bees – of which more in a future post – and they will be sealed with mud rather than leaves. And some of the tubes will attract ‘cuckoos’ of various kinds, notably Sharp-tailed Bees which lay their eggs in leafcutter cells (again, a future post). In my opinion these are as much worth having as the leafcutters themselves.
Leafcutter bees love dry, rotting wood and I have found that a woodpile nearby greatly improves their habitat and increases their numbers. They will sun themselves on it and even find holes in which to nest. It’s best to stack the logs on end so that rain drains off quickly.
In my garden the large leafcutter finds pollen and nectar from Spear Thistle (the favourite), Knapweed, Scabious, Meadow Cranesbill and Borage at different stages in the season. Unlike honeybee workers the females collect pollen not on their hind-legs but with a brush on the underside of their abdomen, which is unusually mobile.
Nest-building activity seems to reach a maximum in the first two weeks of July. You will see the female flying in every few minutes with her leaf discs, fitting them in the tube and dashing off for more until she fits the final disc on the end.
So far, I have no idea whether, having finished stocking a tube with nest cells, a female leafcutter will then go on to stock others, or whether, job done, she retires or dies of exhaustion. I would welcome observations on this.