Last year (2012) I set up my first "bee hotel". I had some success with around fifteen nests completed by Red Mason Bees - [i]Osmia bicornis[/i] (=[i]Osmia rufa[/i]) and one by [i]Osmia leaiana[/i]. Red Mason Bee males started emerging in early May this year, followed by females a few days later. I didn't see the [i]Osmia leaiana[/i] emerging. [img align=left]/imgs/news/21826_6057825055203be14b8996.jpg[/img][img align=left]/imgs/news/21826_18527805375203be12f25ee.jpg[/img]There was lots of activity as the Red Mason Bees started creating new nests; that's all finished now. There are about ten completed nests. What's encouraging is that there is increased [i]Osmia leaiana[/i] activity this year. [i]Osmia leaiana[/i], together with [i]Osmia caerulescens[/i], is one of the two smaller (smaller than [i]Osmia bicornis[/i]) Osmia bees that may regularly be found in gardens. In the UK it is restricted to England and Wales and is on the wing from May to August. It nests in walls, cliffs and old wood, and will also use garden "bee hotels". Like all [i]Osmia[/i] bees, their scopa (pollen-collecting hairs) is situated under the abdomen (not on the hind legs like honeybees and bumble bees). The colour of the scopal hairs can be useful in differentiating the species. In [i]Osmia leaiana[/i], the hairs are all bright orange. The top image, shows an [i]Osmia leaiana[/i] female looking out of her nest hole. They will normally "roost" in these overnight (or when the weather is cold/wet). They will then loiter at the entrance waiting for the sunshine. Unlike [i]Osmia bicornis[/i] which seals its nest holes with mud, [i]Osmia leaiana[/i] (and [i]Osmia caerulescens[/i]) use chewed leaves. This can be seen in the second image. The left-hand nest has been sealed with leaves and the right-hand ones, with mud. The difference becomes less apparent with age, as the leaves turn brown.
[img align=left]/imgs/news/21826_4231854945205160f0844f.jpg[/img][img align=left]/imgs/news/21826_7195219105203be144adc0.jpg[/img]This though, is the first year that I've had a leafcutter bee using the "bee hotel". There are seven species of UK leaf-cutter bees, all in the genus [i]Megachile[/i]. They are medium to large and like [i]Osmia[/i] bees, have the scopa under the abdomen. The colouration of the scopal hairs are again, a useful differential aid. I first saw this leaf-cutter looking out of a hole. It looked slightly different from the [i]Osmia leaiana[/i] females, the facial hairs being paler and the overall size, larger (the images are not to the same scale!). Once she emerged from the hole, I could see that the head was also proportionately smaller (in relation to the body) than in [i]Osmia leaiana[/i] although the scopal hairs were bright orange too. The differences are subtle, but any doubt was eliminated when I saw her returning to the nest with pieces of cut leaf and petal. All leaf-cutter bees use pieces of leaf and petal to line their nests and to create the divisions between the brood chambers. I've watched them cutting leaves in the past, and it takes just a few seconds. They typically cut the pieces from the edge of the leaves (they seem to like roses and fuchsias in our garden), and then fly back to the nest with the leaf fragment held by their mandibles and front legs. Some observers have reported them cutting oval sections for lining the nests and round sections for chamber dividers and for the external seal. This one worked industriously, returning every minute or so. I was able to wait with my camera ready, for this "aerial" shot. She's now started on another nest, in an adjacent hole in the "bee hotel".
[img align=left]/imgs/news/21826_8334753795205353eb7184.jpg[/img]Like with many solitary bees, leaf-cutter nests are prone to parasitism by other bee species. Surprisingly, around a third of our solitary bee species are parasites of other bees! This takes the form of cleptoparasitism, where the parasitic species lays its eggs in the nests of the host, thereby "stealing" the nest and food supplies. Such bees are often referred to a "cuckoo" bees. Leaf-cutters have specific cleptoparasites, the [i]Coelioxys[/i] or sharp-tailed bees. There are just a few species of UK [i]Coelioxys[/i] bee and all are scarce. As a bee "enthusiast", it's one of those that I'm always on the lookout for. I've had one previous sighting; this is the second. I just happened to be passing my "bee hotel" and saw it sitting on the top. I rushed indoors for my camera and returned, expecting it to have gone. Fortunately, it was still there and I got a couple of good shots. I saw it once more later the same day. Haven't seen it since, but still looking! The female [i]Coelioxys[/i] uses her pointed abdomen to cut through the leaf seals separating the brood chamber and then lays her egg inside. The parasitic larva consumes the host egg/larva and the food stores and develops into an adult. It emerges the following year.

An nesting aggregation of Mellinus arvensis Wasps

A Bee Hotel Update