Committee on the Status of Species at Risk in Ontario (COSSARO)
Assessed June 2010 by COSSARO as Endangered
June 2010

Part 1: COSSARO candidate species at risk evaluation form – June 2010

Rusty-patched Bumble Bee (Bombus affinis)

Current Designations:

NRANK Canada – N1
COSEWIC – Recommended status - Endangered
SARA –No schedule, No Status
General Status Canada – No Status ESA 2007 – No Status
General Status Ontario – No Status

Distribution and Status Outside Ontario:

From southern Ontario (essentially Algonquin Park south) and southwestern Quebec south to Georgia and west to the Dakotas. In the southern parts of its range it occurs primarily at high elevations. Declines have been noted throughout the range. Although the species has no formal state or federal SAR status in the US, it is listed on the on the Xerces Society’s red-list of pollinator insects as 'Imperiled (Thorpe and Shepherd, 2005).

Eligibility criteria

Native Status


Taxonomic Distinctness


Designatable Units


Priority-setting criteria

Recent Arrival


Primary criteria (rarity and declines)

  1. Global Rank
    Not in any category. Ranked as GU (Unrankable) due to a lack of information about the species' distribution and occurrence.
  2. Global Decline
    EN. There is a generally recognized range-wide population decline.
  3. Northeastern North America Ranks
    EN. The species is currently ranked as S1 or SH in 89% of the northeastern North American jurisdictions in which it occurs or has occurred
  4. Northeastern North America Decline
    EN. There is an unquantified but generally recognized northeastern North American population decline (Colla and Packer 2008; Evans et al. 2008).
  5. Ontario Occurrences
    EN. Only known from a few recent records
  6. Ontario Decline
    EN. Virtually disappeared over a 20 year period
  7. Ontario’s Conservation Responsibility
    Not in any category. We are at the northern edge of the extensive range

Secondary criteria (threats and vulnerability)

  1. Population Sustainability
    EN. Numbers are apparently very low
  2. Lack of Regulatory Protection for Exploited Wild Populations
    Not in any category.
  3. Human Threats
    Not in any category. Difficult to assess, but habitat alteration and movement of domestic bumblebee colonies are potentially important.
  4. Specialized Life History or Habitat-use Characteristic
    Not in any category. Nest sites or microclimate might be limiting, but this information is not available.
  5. Mortality Trends
    EN. Pesticides and pathogen spillover have been suggested as possible causes of the decline.

COSSARO criteria met (primary/secondary)

Endangered – [5/2]
Threatened – [0/0]
Special concern – [0/0]


This species has undergone a well-documented and precipitous decline throughout its range, for reasons unknown. Pesticides and pathogen spillover have been suggested as possible causes of the decline. At the same time some other Bombus species have become much more common and others, such as B. fervidus, have become less common. We have an excellent baseline from which to work in the form of extensive collections, theses and papers made by D.H. Pengelly and his students in the 1970s. Recent surveys by Colla et al. (2008) and others have utilized the same sites studied by the Pengelly group, and have been able to show striking declines.

Information sources

Colla, S.R. and L. Packer. 2008. Evidence for the decline of Eastern North American Bumblebees, with special focus on Bombus affinis Cresson. Biodiversity and Conservation 17:1379-1391

Evans, E., Thorp, R., Jepson, S., and S.H. Black. 2008. Status review of three formerly common species of bumblebee in the subgenus Bombus. Prepared for the Xerces Society for Invertebrate Conservation. [Online]

Appendix 1

Northeastern North America rank, status and decline

CTNot present
DENot present
LBNot present
MBNot present
NBNot present
NFNot present
NSNot present
PENot present
RINot present
WVNot present

Occurs as a native species in 19 of 29 northeastern jurisdictions SRANK or equivalent information available for 17 of 19 jurisdictions = (89%) S1, S2, SH, or SX in 17 of 19 = (89%)

Part 2: Ontario evaluation using COSEWIC criteria

Regional (Ontario) COSEWIC Criteria Assessment

Criterion A – Declining Population

Yes [EN]. The species has declined dramatically since the 1980's but the exact timing of the decline within a single ten year period is unknown.

Criterion B – Small Distribution and Decline or Fluctuation

Yes [EN]. The EO and IAO are both 4 km2 (B1 and B2). The species has been found only at one site since the 1990's despite repeated searches for it throughout its previous Canadian range (B1a, B2a). Continuing decline in EO, IAO, number of locations and number of individuals is expected based upon any of the known threats (B1b(i, ii, iv, v), B2b(i, ii, iv, v)). Decline in habitat is also probable (B1b(iii) and B2b(iii)) but is less certain.

Criterion C – Small Population Size and Decline

Yes [EN]. The population size unknown but decline is certain. Small and Declining Number of Mature Individuals): The total number of individuals remains unknown, although is certainly very small and probably less than the 2,500 threshold for endangered but this cannot be stated with certainty.

Criterion D – Very Small or Restricted

Insufficient Information. Total population size is unknown.

Criterion E – Quantitative Analysis

NA. Quantitative Analysis: Not performed.

Rescue Effect

No. Problem exists in entire range