Very small brown bumblebees

[Bumblehawks]

Hi there,

On a site which has Bombus ruderatus (Ruderal bumblebees) and Bombus ruderarius, (red shank carders) we also found some tiny brown bumblebees feeding on red bartsia. They looked similar to B. muscorum, (Common carders)- could they possibly be B. humilis though due to their tiny size? Its hard to describe them in terms of mm, but they looked as small as bumblebees can get!

I'd really appreciate any help- ID guides don't talk much about using size as a part of identifying bumblebees.

[Matt Smith]

By the sound of it, they are just small workers, all of the Carder Bee species can produce workers from "tiny" to "large" depending on how well fed that particular brood were, so size is not a helpful guide to species.

Best way to see if these are B.humilis is to take a couple of voucher specimens and check them carefully under a scope, separating the 2 less common "orange" Carder Bees in the field is very difficult.