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Bombus affinis by USFWS

Bumblebees of the World Blog Series… #3 Bombus affinis

The Rusty patched bumblebee, Bombus affinis

By Elizabeth Franklin, Bumblebee Researcher, Guelph, Canada

This month’s Bumblebees of the World blog is written by Bumblebee Researcher, Elizabeth Franklin, from the University of Guelph, who focuses on the plight of a critically endangered bumblebee in North America.

Fact File

Latin name: Bombus affinis

Common names: Rusty patched bumblebee

Colour pattern: Workers, queens and males have a yellow collar, black band or circle followed by another yellow band on the thorax. Workers and queens have two, mostly yellow bands at the top of the abdomen whereas males have a rusty patch on the top of their abdomen giving the species its name.

Favoured flowers: Generalist but reported on hyssops, prairie clovers, sunflowers, blueberries, the apple family and goldenrods.

Global region: East Nearctic region (North American temperate region)

Geographic distribution: Canada (Ontario), United States (Wisconsin, Virginia, Tennessee, Ohio, Iowa, Indiana, Illinois, Connecticut, Maryland, Massachusetts, Minnesota)

Conservation status: Critically Endangered

Bombus affinis or the Rusty patch bumblebee is a large, short tongued, bumblebee that was, until relatively recently, abundant throughout its range in North America and Canada. Like many other bumblebees, it nests in underground cavities but its queens emerge earlier than those of many other North American bumblebee species. Bombus affinis used to be so abundant that there are reports of them within Toronto. However, Bombus affinis has now been recognised as Critically Endangered by the ICUN after an >80% decrease in its former range. Its endangered status has been recognised in Canada since 2014 and the United States since 2017. Bombus affinis is the first bumblebee to be recognised as endangered in the United States and this status was only awarded after extensive public petitioning through the Xerces Society.

The reasons for the decline of Bombus affinis are not completely clear but pathogen spill over from managed bumblebees for greenhouse pollination is hypothesized as the major cause. The decline of this bumblebee and its close relatives correlate closely with the timing of increased infection rates of a bee pathogen Nosema bombi, thought to originate from imported commercial bumblebee colonies. In addition, urbanisation, intensification of agriculture, pesticides and climate change are thought to have also contributed to this bumblebee’s decline.

The last recorded sighting of the Rusty patch bumblebee in Canada was in 2009. Since then increased survey efforts have detected Bombus affinis in the Northern United States but have yet to find evidence of this species in its former Canadian range. This increased surveying is largely due to the extensive contributions of citizen scientists sending their photos to Bumblebee Watch for expert validation. Records are collected for all North American bumblebee species but the map below just shows the validated records for Bombus affinis.

The contributions of citizen scientists have allowed experts to find the strong holds of Bombus affinis and protect those populations. These areas and their Bombus affinis populations are now being studied to gain insights into how this species can be conserved and why they are declining elsewhere. In addition to this, scientists and conservation organisations have greatly invested in public engagement, encouraging citizens to grow pollinator gardens and contribute to the Bumblebee Watch programme. The story of Bombus affinis illustrates what we, as the public, can do to raise awareness, protect and hopefully restore our endangered bumblebee species.

Links to further information:

IUCN red list

NHM Bumble bees of the world

Xerces Society Bombus affinis

A ghost in the making: Searching for the Rusty patched Bumblebee