Solitary Bees

The perhaps most noteworthy thing about this project is the access I have to my population of Osmia Rufus / solitary bees / Orchard Mason bees (call them what you like). They do not seem bothered by my presence nor disturbed by the light that floods into the box when I take the lid off. They continue their activities in their transparent tubes. This year the experience has offered me a real surprise…
I have a suspected incident of cannibalism in tube #4! The story goes like this…

More nesting space was urgently needed, so I unblocked some empty tubes

Near the end of the efforts when the last few remaining female bees were finding fewer and fewer tube holes, I decided to intervene and gently open up the outer seal to two or three tubes that contained only one cell or two at the back (bearing in mind that the tube length can accommodate up to five cells). As there was always an inner mud seal to a cell, removing the outer one would not damage, nor render the established cells more vulnerable. At least that was what I thought…
Afterwards, I did not pay that much attention to what was happening in the tubes, I was away in Paris for work.  All I could do was periodically return to take a snapshots of the box developments – the adult bees had finished their work and perished exhausted.  I did notice with satisfaction, that the remaining few bees had added more cells to the unblocked tubes and entrances had been re-sealed.

Caterpillar like larvae were discovered

A couple of weeks later I took a photo of the of the box with the lid off. Something caught my eye. The contents in the front cell of the fourth tube from the right were moving; normally, my mason bee larvae do not react to the light. On closer inspection I realised that the cell was stuffed with caterpillar sized larvae.

Caterpillar-like larvae occupy the solitary bee cell

Two weekends later I return and one very large grub-like creature is left, and no sign of the caterpillars. Again, it was quite agitated by the light when I took the box lid off. The only assumption I could make was that the grub was so large because it had eaten its siblings. In the photo below we see it next to an average size developing Mason Bee larva.

The large larva has cannibalised its siblings

A mystery bee, or is it a wasp?

I have no idea what it is – maybe it’s a parasite, maybe it’s another bee.  What is certain is that the transparent-tube method has now offered us an insight into the development of other species. 

The cannibal's cocoon

A month or two later the larva had spun it’s cocoon (above). Understandably it is a much larger cocoon. 

Time to let nature take its course

The trick will be to see what emerges.  I plan to remove the tube and place it in a clear container to see if I can capture the emergence of the species that is responsible for it.  All that is left to say is ‘watch this space’ (or subscribe to the RSS feed).