Leafcutter bees

How to recognise it

Roughly honey bee sized, dark, with a broad head and conspicuously large mandibles. The abdomen is somewhat flattened and often held tilted upwards. Females carry bright pollen on the abdominal underside, which can make a returning bee look as though it has an orange belly.

• Large mandibles and a broad, blocky head — the leaf-cutting equipment is visible.
• Pollen on the underside of the abdomen, as in mason bees.
• Often seen flying with a rolled green leaf disc held beneath the body, which is unmistakable.
• Summer-active, from June onwards — mason bees are already finished by then.

Body length 7–18 mm (typically 12 mm).

Biology

Social organisation

Solitary

Each female builds and provisions her own nest with no workers and no caste. Most of the world's bee species.

Nesting

Existing cavities and tubes; Hollow stems and plant cavities; Burrows in the ground

Mostly existing cavities — hollow stems, beetle holes, wall gaps, bee hotels, and occasionally rolled-up spaces in soil or rotting wood. Each cell is a leaf-lined capsule containing a pollen and nectar loaf and one egg, sealed with circular leaf discs cut specifically for the purpose. The bee cuts the oval side pieces and the round end caps to different shapes, which is a genuinely impressive piece of behaviour to watch.

Carries pollen

Scopa on the underside of the abdomen

On the wing

June to September

Lifecycle

1. 1EmergenceAdults emerge in early summer, males a few days ahead of females.June to July in temperate regions.
2. 2NestingThe female works alone for four to six weeks, cutting leaves, provisioning cells and sealing them. A single nest tube may hold six to fifteen cells.Four to six weeks.
3. 3OverwinteringLarvae complete development and overwinter as prepupae inside their leaf capsules, pupating and emerging the following summer.Roughly ten months.

Where it lives and what it does

Habitat

Gardens, hedgerows, woodland edge, grassland, brownfield sites and farmland.

Distribution

Worldwide, on every continent except Antarctica, with the greatest diversity in warm dry regions.

Behaviour

Leaf selection is specific: smooth, pliable leaves of a particular thickness, which is why roses, lilac, wisteria and birch are so consistently chosen while tougher-leaved plants nearby are ignored. The cutting takes only a few seconds. Foraging flight is fast and direct, and like mason bees they carry pollen dry, so a great deal of it transfers to the next flower.

Pollination role

Very efficient, for the same physical reason as mason bees: dry abdominal pollen sheds readily. Megachile rotundata, the alfalfa leafcutter bee, is managed at industrial scale for lucerne seed production in North America because honey bees pollinate alfalfa badly — the flower's tripping mechanism strikes them on the head, and they learn to avoid it. Leafcutters are undeterred.

What it forages on

Strongly favours pea-family plants — vetches, clovers, bird's-foot trefoil, lucerne — along with composites like knapweed and thistle.

Honey

Produces no honey

Relationship with people

How people interact with it

Managed commercially in North America for alfalfa seed, in an operation involving hundreds of millions of bees a year and nesting boards rather than hives. In gardens, the leaf notching is the only thing most people ever notice, and it is worth saying plainly that it does not harm the plant.

Management

Uses bee hotels readily, generally preferring slightly larger tubes than mason bees. The same hygiene rules apply.

Conservation

Not threatened as a genus, though individual species are. The commercial alfalfa leafcutter bee has been moved around the world and carries its own disease and escape concerns.