A guest posting from Andrew William Kirkland
When discussing bees, we tend to imagine social bees such as the physics-defying flight of bumblebees or honeybee hives filled with honey. However, of the 267 bee species that call the UK their home, over 90% are friendly solitary bees. With bee and invertebrate abundance declines reported globally, there has been a popular rise in the use of bee hotels to support conservation efforts of bees. However, their design and management could cause more harm than good. Read on to learn more about solitary bees, the pitfalls of bee hotels and the simple steps we can take to avoid them and promote better bee conservation.
A solitary bee’s life
As the name suggests, solitary bees don’t characteristically live in social hives and given their vast species diversity, there is a vast variety of nesting behaviour and habitats. However, typically an adult solitary bee emerges in the spring from its own tunnel nest dug into either the soil or from a tunnel nest fashioned from an abandoned mouse nest. Whereas other solitary bees will create nests from tunnels produced by wood-boring beetles in trees and deadwood, bramble stems or even snail shells. First to appear are males, which feed on pollen whilst waiting for females to emerge and mate with. After mating, females will then seek out a nest site and lay eggs in cells with female eggs placed towards the rear and males towards the front. Each cell is provided with a pollen loaf for the larvae to feed on, which for mason bees, necessitates 1, 875 flower visits per loaf, therefore, it’s easy to see why bees contribute to the pollination of 1/3 of our food crops! Each egg is then sealed in a cell by using differing materials, such as leaves by the leafcutter bee (Megachile centuncularis) whereas the red mason bee (Osmia bicornis) uses mud.
The problem with garden centre bee hotels
The first issue with bee hotels is that most of our native bee species are ground-nesting. Therefore, a standard garden centre bee hotel comprising of tunnels made from plastic, glass, cardboard or bamboo canes which is then hung on a fence is not an attractive nest for many bees. However, they do attract mason bees, yet the often-poorly designed hotel can be fatal to potential guests. A lack of overhang to disperse rainwater and the use of plastic and cardboard tubes increase the opportunity for condensation and contributes towards the spread of fungus, disease and parasites.
Where suitable nesting tubes are used such as bamboo canes, often they are too short in length, with too large a diameter and contain splinters. Tubes with a diameter greater than 10 mm are too large and are unlikely to be used, whilst splinters deter bees due to the potential damage they can cause to their delicate wings. Whereas tubes with a length less than 6” might not deter occupation yet it can lead to offspring imbalances for the ratio of males and females, which can impact conservation.
You are the manager of the bee hotel
Garden bought bee hotels often come without any instruction and to avoid creating a bee version of ‘Fawlty Towers’, it is necessary to understand siting and maintenance requirements, thankfully these are easy.
Bee hotels should be deployed in the spring facing south-southeast to catch the morning sun and elevated off the ground without any vegetation pressing against the hotel. This will help bees stay warm and allow them to fly for longer whilst limiting access for potential predators or pests. When a site is chosen, make sure that the hotel is fastened securely, as otherwise this can discourage nesting or can dislodge established nests during windy weather. Now that the hotel is secured it is time to consider seasonal maintenance.
In the spring and summer bees are busy collecting pollen and nectar, therefore, you can support them by planting pollen-rich native plants and limiting the use of pesticides. This is also a great opportunity to check your garden and hotel for signs of nesting, which can be recorded as part of a UK wide monitoring scheme. For any pre-existing hotels from the previous season, late-spring is the time to clean hotels and replace tunnels with new tubes as bees can’t clean detritus and this will prolong the use of hotels and reduce the spread of pests and disease. Finally, towards the end of autumn, place hotels inside a shed to shelter the nests from the ravages of UK winters and then return them outside in early spring – this is a critically important aspect that is often overlooked.
Ultimately regardless of good maintenance and management, bee hotels will eventually rot as they are made from natural materials and will require replacement. However, this presents an opportunity to use old hotels as part of a bug hotel or as composting material whilst a new bee hotel can be built as a replacement, either a freestanding or ground-nesting variety (or both).
DIY: simple and satisfying
The simplest nesting tube style of DIY bee hotel involves drilling 6” holes of varying diameters from 2-10 mm into a block of untreated wood, which can be fastened to a fence, post, wall or tree with a southerly aspect. Remember to include a sloping lip to shed rainwater and to have one hole per nest tube which can be sand-papered or counter-sunk to remove splinters. This style of bee hotel can also benefit from using specially designed paper and cardboard tubes, which can be replaced to improve hotel longevity.
To support ground-nesting bumblebees, a simple nest can be created by partially submerging an upturned clay pot in the ground containing dry nesting material such as a mouse nest or straw and have it connected to the soil surface via a length of hosepipe which mimics a tunnel. An even simpler method which can support mining and mason bees is merely providing access to a patch of soil clear of vegetation. This soil can be used as a mud quarry to line nesting cells or could be used directly to produce ground nests.