Tuesday, May 08, 2007

Mason Bees

This picture was taken on the 15th April and shows a female Mason Bee or Osmia Rufa entering her nest hole in my Bee and Ladybird Box. They are a solitary bee (no hive or queen) and every female is fertile and makes her nest usually in holes abandoned by a variety of wood borers.

In the deepest part of the hole they form an egg chamber, collect a loaf of pollen and nectar, lay an egg on the pollen and then creates a partition with mud. They repeat this process until the hole is full of egg chambers. Female -destined eggs are laid in the back of the chambers and male eggs towards the front. She then plugs the entrance to the tube with mud.

These hard-working little bees only live for up to eight weeks in the spring from the middle of March to the middle of May. By the summer, and after moulting 4 or 5 times, the full grown larvae has consumed all of its provisions and begins spinning a cocoon around itself and enters the pupal stage. The new adults form in September and remain in the cocoon until the following spring when the new generation of adults emerge. The males are the first to come out and they remain near the nests waiting for the females. When the females emerge, the first thing they do is mate. The males die and the females begin provisioning their nests, and the cycle begins again.

These two pictures show the state of the nest box on the 15th April and the 19th May. It can clearly be seen that between the two dates, 15 of the holes have been sealed up with mud. It will be interesting next spring to see how many of these holes are opened and whether the same ones are ever used again.