By Suzanne Rex, Conservation & Volunteer Assistant
I began working at the Bumblebee Conservation Trust in February 2016, answering a number of enquiries and helping out in the office. Starting this job with little knowledge about bumblebees and other pollinators, I have been required to research a great deal of information for email replies. This opened my eyes to the huge diversity and importance of pollinators. One group of bees which I found particularly interesting were Leaf-cutter bees, which is why I decided to write a blog about them.
Leaf-cutter bee (Megachile sp.) in a nest. Photo: Anne Donelly
As well as the social living bumblebees and honeybees, there are over 225 species of Solitary bees pollinating the UK. They are called solitary bees as they have no social caste and basically fend for themselves and their offspring. Leaf-cutter bees belong to the Megachilidae family, and are a fantastic pollinating group for a variety of fruit, veg and other plants including wildflowers.
Some species, like the Silvery leaf-cutter bee (Megachile leachella) and the Coast leaf-cutter bee (Megachile maritima) can be found nesting in groups called aggregations, although each female tends to their own nest cells. However, most species choose to nest in existing cavities on their own. Leaf-cutters have been found to nest in a variety of places such as dead wood, hollow plant stems, cavities in walls and occasionally in the soil. Commonly found in gardens, these bees are widespread across the UK, though they have a smaller presence in the north.
One of the most common species of Leaf-cutter bee is the Patchwork leaf-cutter (Megachile centuncularis). Patchwork leafcutters look similar to honeybees, though the females have a patch of hair beneath their abdomen called a pollen brush. The pollen brush is used for storing pollen, as opposed to most other bees which store pollen in pollen baskets on their hind legs. Intriguingly, some Leaf-cutter species including Patchwork leaf-cutters lift their abdomen up into the air while feeding; see this video to watch this distinctive foraging behaviour. However, they are probably best known for their trick of cutting neat, semi-circular pieces out of rose and wisteria leaves to take to their nests. These bees will grasp the leaf cutting and carry it underneath their body to their nest. The Patchwork leaf-cutter will glue the overlapping pieces of leaf together with saliva to use as lining, in order to build individual cells for their eggs which are sealed off by more pieces of leaf. Within each cell, the egg is provisioned with pollen to provide the hatched larvae with essentials to grow. This pollen can come from a variety of flowers including legumes like runner beans, as well as berry flowers like brambles. The larvae will then pupate into adults in autumn and hibernate inside their cells over winter.
left Black-headed leaf-cutter (Megachile circumcincta) male. Photo: Steven Falk
right Patchwork leaf-cutter (Megachile centuncularis) cutting a leaf. Photo: Bernhard Plank
Make a home for the bees
Like many solitary bees, Leaf-cutters can be limited by the amount of available nesting habitats. The good news is that this is something we can all easily do something about – by creating a bee hotel. Leaf-cutters and other solitary bees are great for pollinating your fruit and veg, so why not help them out and entice those that like to nest in cavities into your garden? Bee hotels are great to watch, provide lots of entertainment and are available to buy in most garden centres. You can also make one yourself which is cheap and easy. For 5-star accommodation all you need to do is find an untreated block of wood and drill holes of varying diameters into it (2-10mm), but not all the way through the wood. Try and make the holes as smooth and splinter-free as possible, as splinters can damage their wings. It is also important that rain does not get into it so the gaps should be created at a slight incline. The hotel should then be propped up or mounted onto a sunny, south facing wall and at least a metre off the ground. Another option is to find sections of old, hollow bamboo canes (around 20-30cm long). Tie the bamboo sections together, or place them into a plastic drinks bottle with both ends cut, and hang them horizontally in a sunny and sheltered position.
Many bee hotel designs and ideas can be found on the internet to help. It is best to replace the holes in your hotel every two years, as this prevents the build-up of fungus and parasites. Patchwork leaf-cutter can be seen between mid-June to early September, so if you can set up a home for the bees soon, you may find it is used this year. If not, it will be ready for next year’s bee season in spring!