Indigenous wasps dominate bee hotels

A study by researchers at York University in Toronto found that indigenous wasps were more abundant than both indigenous and introduced bees in bee hotels. These wasps occupied nearly three-quarters of the hotels each year, according to the research published in PLOS ONE in 2015.

Study spanned three years and many locations

The study monitored nearly 600 bee hotels in gardens, parks, and on rooftops over three years. Researchers identified more than 27,275 bees and wasps, tracking about 200 hotels annually between 2011 and 2013. Each hotel was placed at least 250 meters apart in urban areas.

Data collection involved careful analysis

To analyze the data, researchers transferred brood cells into a controlled incubation room set at 26 degrees Celsius and 60 percent humidity. They waited for the adults to emerge, then identified and sexed each individual. This process allowed for precise tracking of species and their nesting habits.

Indigenous wasps outcompeted bees

Indigenous wasps dominated the bee hotels, occupying nearly three-quarters of them each year. A gardener opening the tubes at the end of the season would likely find more wasp cells than bee cells. However, this was an average across Toronto, and not all hotels were the same.

Introduced bees and parasitism risks

Indigenous bees were more likely to be parasitized than introduced bees. Female introduced bees also provisioned their nests with more female larvae each year. Introduced wasps were the only group showing a significant increase in abundance over time. The study warned that grouping cavities in hotels could create a "communal buffet" for parasites.

Bee hotels may not help endangered species

A British summary of the study suggested that bee hotels might act as traps for threatened species rather than supporting them. This idea, however, was not tested in the Toronto study. Most bees actually nest in the ground, and the focus on hotels may have shifted attention from their natural habitats.

Critics warn of misleading marketing

The study authors introduced the term "bee-washing" to describe the false claims made by some sellers of bee hotels. These claims suggest the devices support wild bees, but the research found no evidence to support this. The authors urged more research and emphasized the importance of proper maintenance and tube selection in bee hotels.

Findings are specific to Toronto’s environment

The study was conducted in Canada, with its specific species and climate. A follow-up study by the same authors in 2016 focused on solitary bees in nesting boxes. While the Toronto results cannot be directly applied elsewhere, they highlight the need to examine local bee hotel usage carefully.

Existing bee hotels should be observed

For those who already have bee hotels, the study suggests observing them before discarding them. Checking for signs of use, like blocked entrances or nesting activity, can help determine their effectiveness. Models with removable tubes should be checked at the end of the season, while others should be replaced rather than left to decay.

Bee hotels originated in agriculture

The concept of bee hotels dates back to the 1950s, when they were used to transport alfalfa leafcutter bees in stackable containers. Initially designed for agricultural purposes, they were later promoted as tools for nature conservation without evidence of their ecological benefits.