Mason Bees – The Last Post

Not another post on bees. Well don’t blame me, blame Pam! Another of my natural history heroes is Gilbert White (1720-1793). He only wrote one book “The Natural History and Antiquities of Selborne”. He is known for his meticulous observation and documentation of Nature. Although he was one of the first to observe migration in birds it is interesting to follow his comments on swallows. White writes to his brother in Gibraltar and asks questions about the movement of birds across to Africa. He notes down his own sightings of swallows in early spring and  early winter. At the same time he receives notes from others –

“Another intelligent person has informed me that, while he was a schoolboy at Brighthelmstone, in Sussex, a great fragment of the chalk-cliff fell down one stormy winter on the beach and that many people found swallows among the rubbish but, on my questioning him whether he saw any of those birds himself; to my no small disappointment, he answered me in the negative ; but that others assured him they did.”

There was a general belief that swallows went into a “torpid state” in winter and hibernated in holes in cliffs and buildings, much like bats do. White struggled to get the evidence that he needed for migrations – no bird rings, no army of birdwatchers with notebooks and definitely no birds fitted with GPS tracking devices. But he was always looking and gathering information.

So, when Pam contacted me to tell me that she had been watching the bees in her own bee hotel but they had all now gone,  she asked a simple and straightforward question. What’s happened, where have they all gone? My reply was also simple and straightforward. The males die when they have done their stuff and the females die after laying their eggs. The End. But after a few days I started to realise how unsatisfactory my answer was. Although I think it is true and perhaps I read it somewhere, but how do I know they are dead. And what do they die of? What evidence do I have that they are dead? To turn the question on its head – why don’t the bees feed up on all of the lovely nectar in our gardens and repeat the whole business again later in the year? Why not feed up, go into diapause and overwinter and do it all again next spring! We know very little about the natural history of death. Sorry Pam.

But at least we can follow what is going on in the bee tubes. In some of the tubes it is possible to see the white bee larva. One was still feeding and others were weaving a rough cocoon of white strands (silk?). Others had completed this stage and are now inside a tough brown pupa. The bees will remain in this state until next April/May when they will emerge and start the process again. A mason bee’s life consists of over 10 months as egg, larva, and pupa and less than two months as a flying adult (according to the books!). But what about those cells filled with yellow strands? The bee larva has been killed and partially eaten and the food store put in for the bee by the female is being consumed.

The new inhabitants of the cell are fly larvae (6-7). I assume that these are the larvae of the flies that I mentioned in a earlier post. I guess the yellow strands are the faeces of the larvae but it all looks very strange to me. Now wouldn’t it be good if I could get a parasitic wasp out of the flies!

Of course, there is loads more to find out about these mason bees. I have some specimens of the parasitoids and the fly to send to experts to get them properly identified but I don’t expect answers until much later this year. And I am still waiting for my first leaf cutter bee to appear. Thanks to Sally for the photographs and thanks to others for bits of video, photographs and comments. One of Gilbert White’s most famous quotes –

“It is I find in zoology as it is in botany: all nature is so full that that district produces the greatest variety which is the most examined”. I have really enjoyed this lockdown project.

Malcolm