Insect nesting boxes, sometimes called “insect hotels,” aim at boosting the number and diversity of insects in the environment. They have become a common sight in vegetable gardens, parks and green lanes. And yet although they are popular, not much is known about how effective they are. That’s why the Insectarium conducted a research project to identify the species that call these structures home. Here are a few of the findings.
How did we proceed?
For this project, we installed 60 nesting boxes in Montréal in summer 2020. They were made of hollow reed stems and wood logs with holes of various diameters. In cooperation with citizens’ committees and the boroughs of Mercier–Hochelaga-Maisonneuve and Rosemont–La-Petite-Patrie, 20 boxes were installed in green lanes, 20 in community gardens and another 20 at the Botanical Garden. They were all brought back to the Botanical Garden in the fall to spend the winter under the snow. Then, in the spring, they were placed in a greenhouse. The insects were subsequently preserved so that they could be identified in the lab.
A wide variety of occupants
All in all, 682 hymenoptera from 16 different families emerged from their “hotels.” Most of these were native species, with the majority being solitary wasps. One third of the species were bees, predominantly leafcutting bees. Predators made up half of the insects, while pollinators made up a third, followed by parasitoids and kleptoparasites. Kleptoparasites are insects that enter their host’s nests and eat their food reserves. This breakdown of insect species was similar to that found by researchers in Toronto.
The logs were occupied by a greater number of insects, which were also more diverse. Leafcutting bees tended to prefer larger holes, ranging from 5 to 8 mm in diameter, but both the small and large holes were used by a similar diversity of insect species, regardless of the material used.
Not just pollinators!
Insect nesting boxes are often thought of as a way to help pollinators, which are so important to plant reproduction. However, our research shows that they are not the only insects to benefit. A number of predatory wasps also use them to lay their eggs. These predators play a valuable role in controlling insects that are unwanted in our gardens. For example, aphid wasps—which make up many of the “guests” at our insect hotels—hunt aphids and are an important ally in the fight against crop pests.
Homes in high demand
Our findings show that nesting boxes are frequented by many species of hymenoptera, which have complementary ecological roles. Logs with holes are the recommended building material, provided they are properly maintained. If you want to attract a variety of species, make holes of different diameters (from 3 to 10 mm) to meet the needs of small and large species alike.