There are an estimated 25,000 different species of bee on Planet Earth and they come in many different shapes and sizes. The largest bee in the world is 'Wallace’s Giant Bee' (Megachile pluto). She grows up to 3.9 cm long and has a wingspan of 6.3 cm. The smallest bee in the world is 'Perdita minima'. She is less than 2 mm long.
Bees also have different length tongues (proboscis). Tongue lengths vary from around 0.5mm to 15mm in Britain and Ireland
The size of the bee and the length of her tongue, are both of great significance when it comes to which flowers she is able to access when foraging for pollen and nectar. Honeybees tongues are around 6.3mm in length - so they can only access flowers with fairly short corollas.
If you have red and white clover on your lawn, you will notice different bee species on each. Short-tongued bees like honeybees and buff tailed bumblebees will go for the white clover, as it only has a short corolla. However, long tongued bumblebees, like B. hortorum (the Garden bumblebee) will forage on the red clover as it has a very deep corolla.
The deeper the corolla (flower tube) the greater the nectar reward tends to be….so short tongued bees often need to visit more flowers to get the nectar they need.
The bee in the photo above is Bombus hortorum (the Garden Bumblebee). She has the longest tongue of any bee in the UK. If you see a black & yellow striped bumblebee with a white tail on your broad beans, and if her tongue is hanging out as she flies between each flower, it is highly likely to be this bee!
Some bee species resort to ‘robbing’ the nectar by cutting a hole in the base of the flower and accessing it that way. This is known as 'larceny'. When a bee commits larceny, the plant loses out because the bee completely bypasses the flower's pollen. Bombus terrestris (the buff tailed bumblebee) is a notorious nectar robber. Once she has made a hole, other bees and wasps use it to access the plant's nectar. Not a very fair exchange!
More about bumblebee flower preferences here
Photos of largest and smallest bees here