Rusty patched bumblebee

How to recognise it

A medium bumblebee with a yellow thorax carrying a black spot between the wings, and — in workers and males only — a distinct rust-coloured patch in the middle of the second abdominal segment, surrounded by yellow. Queens lack the rusty patch, which catches people out.

• A rust-brown patch on the second abdominal segment, present in workers and males and absent in queens.
• Yellow thorax with a central black spot.
• Range now highly fragmented across the upper midwest and a few eastern sites.
• Any sighting is worth reporting — the species is monitored largely through public records.

Body length 10–20 mm (typically 14 mm).

Biology

Social organisation

Eusocial, colony dies each autumn

A true colony with a queen and workers, but only for one season: everyone dies in autumn except mated new queens, who overwinter alone. Bumblebees.

Colony size at peak

100–400 individuals

Colony lifespan

One season.

Winter

Mated new queens overwinter alone in loose soil or leaf litter.

Castes

Queen, Workers, Males, New queens

Nesting

Burrows in the ground; Existing cavities and tubes

Nests underground, usually in abandoned rodent burrows, and occasionally at the surface under leaf litter.

Carries pollen

Corbicula (pollen basket) on the hind leg

On the wing

April to October

Lifecycle

1. 1Early emergenceQueens emerge early, in April, which historically made it a valuable spring pollinator across its range.April to May.
2. 2Long colony seasonOne of the longer North American bumblebee seasons, running from spring into autumn.
3. 3ReproductionReproductives from late summer into October.

Where it lives and what it does

Habitat

Prairie, woodland edge, farmland, gardens and urban parks — it was a habitat generalist, which is part of what makes the collapse so alarming.

Distribution

Formerly across 28 US states and two Canadian provinces. Now reduced to scattered populations, concentrated in the upper midwest around Minnesota and Wisconsin.

Behaviour

A short-tongued generalist with an early emergence and a long season, which historically made it one of the most useful wild pollinators in the eastern United States. Nothing about its ecology explains its collapse; the leading hypotheses involve pathogens rather than habitat alone.

Pollination role

Historically a major pollinator of prairie flora, cranberry, apple, alfalfa and plum. Its functional loss across most of its range is a substantial reduction in wild pollination capacity in eastern North America.

High, and now largely absent from the landscapes where it mattered.

What it forages on

A broad generalist across prairie and orchard flora.

Honey

Keeps only a few days of stores

A few days' worth in wax pots.

Relationship with people

How people interact with it

Its listing in 2017 was the first for any bumblebee in the United States and remains a reference point in pollinator policy. Public sighting records do much of the monitoring, and citizen-science programmes have located several surviving populations.

Conservation

Endangered. The decline coincided closely with the commercial rearing and movement of Bombus impatiens and Bombus occidentalis colonies for glasshouse pollination, and pathogen spillover — particularly of Nosema bombi — is among the leading explanations. Habitat loss and pesticides compound it.