Daylight robbery

I have seen bumblebees robbing nectar from comfrey flowers before but as far as I remember I haven't seen this behaviour from solitary bees.  Nectar robbing is when a bee takes nectar from the flower through a hole bitten in the side rather than entering normally and offering pollination, especially a bee with a tongue too short to reach the nectary.  I suspect the holes were made by bumblebees and the others were just taking advantage.  This is a Buff-tailed Bumblebee

and an Early Bumblebee.

A Common Carder Bee was doing it properly.

This was earlier in the week on the comfrey in the corner of the kitchen garden.  The most numerous bees were male red mason bees.

They were also patrolling the flowers in the vain hope of finding a new female.  In reality all the females are busy provisioning their nests and the males don't have long to live but that didn't stop them challenging and knocking each other off the flowers.

Female red masons were also robbing, obviously getting just nectar here and collecting their pollen elsewhere.

The most surprising to me was a nomad bee, a cuckoo that lays its eggs in solitary bees nests (usually mining bees).

It all goes to show that sometimes crime does pay.  You can read more about the biology of nectar robbing here.

Nectar robbers

If you are a short-tongued bumblebee faced with a long flower you have a problem.  You can't reach the nectaries which are cunningly placed at the base of the flower to make you squeeze past the anthers and stigma(s).  Unless, of course, you cheat.  Comfrey is a very enticing flower but its sweet nectar is out of reach of bees such as this male early bumblebee (Bombus pratorum).  His solution is to use a hole bitten in the side of the flower to steal the nectar without helping with pollination.

If you look carefully you will see that on some comfrey plants every flower has a tiny hole bitten in the side.

Other short-tongued bees that rob nectar include the tree bumblebee (Bombus hypnorum)

and the common carder bee (Bombus pascuorum).

Worker bumblebees vary in side and the smaller ones can get right inside using the correct entrance, like this common carder bee.  It is interesting that there were no holes in the flowers on this plant.

Long-tongued bees like the garden bumblebee (Bombus hortorum) don't have a problem.

Surprisingly the robbing doesn't seem to have much effect on a plant's reproductive success. You can read more about the biology of nectar robbing here.