Bombus ruderarius Müller, 1776

Bombus ruderarius is a medium-small size bumblebee (length in queens: 16-18 mm; length in males 12-14 mm).

The head is moderately elongated, due to the smaller malar gap (which shows a scarce and thin stipple) than the distal width.
Females show a prominent clipeum with thin but dense stipple. The labrum’s groove is shallow and widened at the base, and it shows a shiny forehead. The hind legs doesn’t show reticulated tibias. The genitalia in females is similar to that of Bombus sylvarum.
Males show a long and dense bearded jaw, and a clipeum scarce dotted. The tibias in hind legs are shiny and have long chaetas.