Two-coloured mason bee

How to recognise it

A stocky mason bee with a jet-black head and thorax and a bright orange-red abdomen — the two colours the name records. Females carry pollen dry on the underside of the abdomen.

• Black front half, bright orange-red abdomen. Distinctive and easy.
• Seen entering empty snail shells on chalk grassland in spring.
• Later, seen flying with a grass stem or pine needle held beneath the body — the camouflage behaviour.
• Flies March to June on calcareous grassland.

Body length 10–12 mm (typically 11 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

Nests inside empty snail shells, usually of Cepaea or Helix species, on chalk and limestone grassland. The female provisions cells within the whorls, seals the shell with chewed leaf and mud, frequently rolls it into a more sheltered position, and then constructs a thatched pile of grass stems, pine needles and small twigs over the top — carrying each piece individually in flight.

Carries pollen

Scopa on the underside of the abdomen

On the wing

March to June

Lifecycle

1. 1EmergenceAdults emerge in early spring, males first, on warm chalk grassland.March to April.
2. 2Shell selection and provisioningThe female locates an empty shell, provisions cells inside it with pollen, and seals it.Several weeks.
3. 3CamouflageShe then builds a thatch of grass and needles over the shell, making perhaps dozens of individual flights carrying material. The likely function is concealment from parasites and predators, and possibly temperature regulation.
4. 4OverwinteringThe offspring develop and overwinter inside the shell, emerging the following spring.Roughly ten months.

Where it lives and what it does

Habitat

Chalk and limestone grassland, quarries, coastal cliffs and open woodland edge with abundant empty snail shells.

Distribution

Across Europe. In Britain, largely confined to southern chalk and limestone.

Behaviour

The thatching is the thing worth travelling to see, and it is genuinely observable: a small orange bee repeatedly landing beside a snail shell, dragging a grass stem into position, and flying off for another. Few insect behaviours of this complexity are so easy to watch.

Pollination role

A useful spring pollinator of grassland and scrub flora, and like other mason bees it carries pollen dry and sheds a high proportion of it.

High per individual, as with all abdominal-scopa mason bees.

What it forages on

A generalist on spring grassland and scrub flora, favouring legumes and the rose family.

Honey

Produces no honey

None. One pollen loaf per cell.

Relationship with people

How people interact with it

Almost unknown to the public and a favourite among people who watch bees. It also depends on something nobody thinks to conserve: a supply of empty snail shells, which requires both snails and the predators or weather that leave shells behind.

Conservation

Localised and dependent on calcareous grassland with a good snail population. Grassland improvement removes both the flowers and the shells.