film – Osmia [mason bees hatching]

A few years ago I bought a tube of blue orchard mason bees and what started as 10 bees quickly grew into 100, and now 250 over a couple of years. This year they quickly filled an entire stacking nest block.

Last year, I left the cocoons in cardboard nest tubes until spring. These tubes are a bit of a pain to unravel and I just didn’t get around to in the fall. I usually try to remove them from these tubes in the fall so that none of the bees are lost in the spring due to becoming stuck behind a dead cocoon, and so that I can clean the pollen mites off them, or remove parasitised cocoons. I’ve found the stacking trays much easier to deal with for this reason.

Come springtime, a couple of bees had hatched in the storage area where I keep them, so I brought them all out onto the front step and unwound the tubes and filmed the bees as they emerged from their cocoons. There were quite a few bees in the tubes that had hatched but were stuck behind other unhatched cocoons.

The first bees to emerge are the little males – so the ones seen in this film are all male. Most of the females hatched over the following week. Pollen mites are visible in the pollen mass, and on the bees as well. The dark pellets coating the cocoons is larval bee frass (poop).

Watch in HD on Vimeo.

Part of what I find so interesting about the bees, is all the other insects that use the nest boxes, or parasitise the mason bees.

The first year I raised mason bees, I left the nest box out too late into the summer so when I extracted the cocoons I found that many of them had been invaded by tiny little black parasitic wasps which spilled out of holes in the cocoons in huge numbers.

This year, I opened up a nest tube that had been partly mudded late in the season and discovered it was empty of mason bee larva, but contained the larva and frass of the Cacoxenus indagator fly. I had seen adults hanging around the nest boxes earlier in the year – they look like fruit flies and have red eyes. I believe they might be native to Europe, but appear to be here as well. They lay their eggs in amongst the pollen the female bee provides as food for her larva. The fly larva hatch in the sealed compartments and eat all the larval bee’s food. When the flies hatch in the spring, they bust their way through the mudded tubes by shoving their heads into divots in the mud and inflating them with fluid (haemolymph). There are videos of it, like this one. It’s pretty fascinating.