Yesterday I found a bumble bee nest in an old brick wall (about two metres above the ground). I haven't yet identified the species as the bees tend to fly in and out at high speed. (The flowers below the wall attract more than one species.)

What I could see very clearly however was that as each bee flew in, most of them were carrying in their back legs a small piece of leaf (possibly petal?) a bit less than a square centimetre. The bees which emerged weren't carrying anything, as far as I could see.

I saw this four times over the course of about twenty minutes' observation.

What on Earth would they be doing these leaf fragments?

Mike,

Depending on where exactly you are in the world and what bees (they may not have been bumblebees Bombus per se) you may have seen could alter what my interpretation is.

However, most bees (and for that matter, wasps) are solitary and they go about their lives in different ways. Some are potters (wasps), or mason etc. etc. Google for more about them.

Anyhoo, many solitary bees (and wasps) create linear nests, that is, they lay and egg in a chamber, populate that chamber with a food source (usually a pollen ball) and then seal it. Sometimes wax is used, other times bits of leaf or stone or paper or anything else that is the right size can be used to seal each cell. The female will work down the linear nest (imagine a hollow piece of bamboo or suchlike) creating these cells and dividing them. Obviously, wax and paper that a bee uses can be made to the correct size, as can cut material, like leaves / petals.

Does this help?

It sounds to me like you have watched the nest construction behaviour typical of leaf-cutter bees (Megachile species). There are 9 species in UK, and 2 are certainly common in gardens. These are the large (honey bee sized) Megachile willughbiella (Willoughby's Leaf-cutter), and the smaller Megachile centuncularis.

The former species is a common visitor to various bell flowers (Campanula) and the latter loves Daisy family (Asteraceae).

There are good pics available in the gallery of BWARS at www.bwars.com

It sounds to me like you have watched the nest construction behaviour typical of leaf-cutter bees (Megachile species). There are 9 species in UK, and 2 are certainly common in gardens. These are the large (honey bee sized) Megachile willughbiella (Willoughby's Leaf-cutter), and the smaller Megachile centuncularis.

The former species is a common visitor to various bell flowers (Campanula) and the latter loves Daisy family (Asteraceae).

There are good pics available in the gallery of BWARS at www.bwars.com