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Talkback: The greater bulb fly
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I was shocked the wonderful Japanese roof garden did not get Gold this year as it was so fabulously innovative and interesting and perfect its creator was able to explain it all to us
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Although they lay their eggs on the exposed bulbs at soil level, the bulb fly is not equipped for digging. You are more likely to have found a solitary bee. This large group has several hundred UK species and they vary in size from small bumble down to large ant. Most look like small honeybees. Each female makes a single burrow in the soil, divides it into separate individual cells for her eggs and provisions each with a nectar/pollen cake.
Wasps will invade bee nests, including honeybee hives after brood prey and honey/pollen stores. The bees will defend themselves. I wonder if you have not rather seen something else. Your rust-coloured bees sound like mining bees, Andrena fulva or Osmia rufa. These 'solitary' bees make individual small tunnel nests in the soil, which they stock with nectar and pollen for their grubs. Although they work individually, each female making her own nest burrow, they often colonize an area of bare soil together to make 'bee villages'. The males of both species are much smaller and slimmer than the large, stout, furry females. Could you have been seeing first females, then males?