by Hodge et al.
“Bee hotels” are becoming increasingly popular with members of the public wanting to help wild bees and gain an insight into the natural history of cavity-nesting insects. Equally, similar artificial insect shelters, or trap nests, are being proposed as tools in agri-environment schemes to help farmers augment and monitor insect biodiversity on their farms. Unfortunately, the placing of bee hotels or trap nests does not guarantee their colonisation by breeding bees, and there is currently the need for research exploring how the size, shape, dimensions, and materials used to make bee hotels influences their success. This study used trap nests consisting of plastic pipes filled with cardboard nest tubes to investigate what factors might influence their colonisation by stem-breeding bees and wasps in 16 Irish farms. We found sealed nest tubes at 15 of the 16 farms, and in 37 of 48 individual nests. However, only 7% of the 4800 individual nest tubes were occupied, and only 4% produced cavity-nesting bees or wasps. The following spring, along with a number of bee predators and parasites, we found three cavity nesting bee species (Hylaeus communis, Osmia bicornis, Megachile versicolor) and two solitary wasp species (Ancistrocerus trifasciatus, A. parietinus) had emerged from nest tubes. Each of these species tended to use only a narrow range of nest tube diameters: for example the small yellow faced bee, Hylaeus communis, primarily used nest tubes of 4 mm diameter, whereas the large leaf cutter bee, Megachile versicolor, tended to use nest tubes of 8-10 mm diameter. Further research is still required to examine if making these artificial nests from different materials, such as wood blocks or using bamboo canes, can improve colonisation rates or attract different species of bees or wasps. Overall, however, the results of our study suggest that trap nests offer a valuable tool for ecological research, and to increase the likelihood of bee hotels being used by as many bee and wasp species as possible, they should be constructed to contain a wide size range of nest holes.