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Dear Jaquim,
The main reson for the difference in size in bumle bees is that the queens, which emerge in spring are much larger than workers or males. In Portugal like New Zeland there can be more than one generation of species like Bombus terrestris. Queen bumble bees can wieigh up to a gram from memeory and to overwinter successfully they need about 20% of more of their body weight to be in fat, to ensure they can live through for the about 10 months needed to raise the next lot of new queens. The second photo with a slight yellow places ID in the terrestritirs group in slight doubt and the lower face is too much in the flower in both shots to judge if they have the sort malar space of B. terrestris etc. or the long tongued species, which for instance trend to favour foraging on deeper flowers like Labiatae and honey suckle or red clover.

I worked on bumble bees and their ecolgy in the 1970-1980's including determination of their commercial value for red clover pollination. The white colouring on the abdomen of your specimens distinguishes this species from the variety present in Great britain, New Zealand and tasmania as queens.

Rod Macfarlane