About the Andrena diagnoses

Whether I should feel sheepish or proud, I have spent 1000 hours with Andrena. Yet I am something less than an expert, which I blame on the fact that Andrena is hyper-diverse. One needs a lot of experience to confidently identify one of the 500+ US species. Mentors help: mine include Cody Blacketter and Marisa Fisher of Quamash EcoResearch, and Sam Droege and Clare Maffei of USGS and USFWS. Specimens are essential: my sources include Oregon State University (OSAC), Michigan State University (Rufus Isaacs lab), USGS/USFWS, and others. On this page, I examine some favorite specimens, and walk through my process for identification.

Sources consulted

This resource is not a substitute for expert determination. Its aim is to:
  • Use detailed photos that will help users fine-tune their skill in assessing traits;
  • Model the process of using the scarce resources to inform diagnosis;
  • For the chosen species, provide the evidence that leads to a provisional determination.
  • Tip: Make use of cf. determinations. Say you have an unknown, labeled as "Andrena sp." You compare this to the diagnoses here, and suspect that your specimen is Andrena evoluta. However doubt remains; it is consistent with A. evoluta, but you lack the evidence (or knowledge) to declare that determination for sure. So you label the specimen Andrena cf. evoluta. This is far more informative than "Andrena sp," and it will simplify a later re-examination by you or anyone else. You could also reference the criteria used here with a hyperlink to "https://beeglossary.org/andrena_guide.html#evoluta" (or other species name after the # sign).
Uncredited images are by David Cappaert. I grant permission for any non-commercial use. I've supplemented these with the excellent photos by the USGS/BIML team, and by the Bees of Canada page (Images courtesy of Margarita Miklasevskaja at PCYU with funding from NSERC-CANPOLIN). These public domain images are a huge gift to bee taxonomy.

Related taxonomy pages

Glossary of bee terms
Guide to Andrena on DiscoverLife
Key to Andrena subgenera of the PNW
Endangered plants of the PNW
Key to Lasioglossum of the PPP
Photo blog, 2024, 2025

Note about the DiscoverLife guide: I have spent at least hundreds of hours with the Osmia Temp and Andrena guides. I have also spent a few hours explaining to critics why I believe these are excellent tools. The guides were constructed from existing dichotomous keys, expert knowledge, and specimen examination. So it is incumbent on a critic to point to where these sources are suspect, with the result that the user will declare a species ID that is incorrect. This does in fact happen, but unlike an Osmia key from 1939, the DL key can be updated and illustrated. The greater "problem" in DL is that the trait scoring is incomplete (western species!) and/or overly broad. I.e., the guide is conservative by design. You may not narrow your list beyond a handful of possibles. So you will look elsewhere for finer distinctions. In the context of this diagnosis page, I extensively use the DL guide because:

  1. The interactive nature of the guide permits a user to screen options against traits the user can confidently assess. By contrast, a dichotomous key may require evaluating vague descriptors and comparison to reference material not available. E.g., a couplet that offers alternatives like "hairs dense and long" vs "shorter and sparser" may not be actionable.
  2. The DL guide can quickly rule out many alternatives that don't have to be considered. See above for many examples.
  3. The guide includes species pages. Usually these include text excerpted from primary literature, a range map, host associations, and photographs, all of which might help support or reject a diagnosis.
  4. The DL guides encompass an approach that welcomes participation by a broad community, including citizen scientists. A potential drawback of this is that lowering a barrier might mean lowing the standard. Thus I create documents like this one.

Note about the LaBerge et. al. literature: The papers that have defined the US species of Andrena are epic in scope, based on many thousands of specimens and decades of work. But the species (and subspecies) distinctions made in 1978 are not of course the final word. If a different set of collaborators had run a parallel effort to codify the taxonomy, their final list would be different, based on different instincts regarding the significance of traits, within-species variablility, interpretation of phylogeny, etc. The state of things would be further scrambled with the addition of modern techniques (genomics), accumulating wisdom, and a few additional decades of distribution data.

I have been told that Wally LaBerge did not use his own published keys. He used the versions with penciled-in notes about curious exceptions and puzzling details. I can relate to this.

Update February 3, 2026
David Cappaert, Quamash EcoResearch, cappaert@comcast.net

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