Bumblebees are usually much larger than honeybees and build small nests in compost heaps, under sheds, in loft insulation etc. They also frequently take up residence in bird nest boxes using the old bird nesting material as part of their nest; they are relatively small bumbles bees but can appear to be in large numbers, but no self-respecting honeybee would find a nest box suitable for home – far too small. Leave them be (excuse the pun) and enjoy watching them.
Bumble bees are very beneficial and not a problem if left alone (although they can make a lot of buzzing noise if above your ceiling!). The queens overwinter then set up home in the spring. By early winter she dies as do her workers, her young queens having left to hibernate. For further about these bees see the downloadable leaflet.
Solitary bees can be found living in burrows in lawns, sandy banks, walls and even in the stems of plants. Early in the summer lots of these bees in a lawn or bank can give the appearance of a swarm as many be seen being very busy coming and going like residents in a block flats all leaving to go to work in the morning.