Sea aster bee

How to recognise it

A medium bee closely resembling the ivy bee — gingery-brown furry thorax and a black abdomen with buff hair bands — and separable from it mainly by habitat, timing and, definitively, by genitalia. The two were long confused.

• Found on saltmarsh and coastal grazing marsh, on sea aster.
• Flies late — August into October, overlapping with the ivy bee.
• Gingery thorax with banded abdomen, essentially identical to the ivy bee in the field.
• Nests in large aggregations in sea walls, saltmarsh edges and coastal banks.

Body length 10–14 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

Burrows in the ground

Digs burrows in firm ground above the tide line — sea walls, saltmarsh edges, coastal banks and borrow dykes — and nests in aggregations that can be very large. Cells are lined with the cellophane-like polyester secretion characteristic of Colletes, which waterproofs them in ground that floods.

Carries pollen

Scopa — dense hairs on the hind leg

On the wing

August to October

Lifecycle

1. 1Late emergenceAdults emerge in August, timed to sea aster flowering, with males first.August to September.
2. 2ProvisioningFemales collect sea aster pollen through September and October and die as the plant finishes.Six to eight weeks.
3. 3OverwinteringThe larva develops on its provision and spends most of the year underground in a waterproofed cell.Roughly ten months.

Where it lives and what it does

Habitat

Saltmarsh, coastal grazing marsh, sea walls and estuary edges with abundant sea aster.

Distribution

Southeast England and the adjacent coasts of France, Belgium and the Netherlands. A globally restricted species with a large share of its population in the Thames estuary and Essex marshes.

Behaviour

A near-obligate specialist on sea aster, with the whole life cycle compressed into that plant's flowering. It also faces a constraint few bees do: the nest must be above the tide line and close to a saltmarsh, and rising sea levels and coastal squeeze reduce the ground meeting both conditions.

Pollination role

The principal pollinator of sea aster across its range, and important to a saltmarsh flora with relatively few insect visitors.

High on its host plant and negligible elsewhere.

What it forages on

Sea aster overwhelmingly. Where sea aster is scarce it will use other late composites, but the population depends on the host.

Honey

Produces no honey

None. One pollen provision per cell.

Relationship with people

How people interact with it

A species whose conservation runs directly into coastal engineering. Sea walls provide nest sites and managed realignment schemes that breach them can remove aggregations, while doing nothing risks the saltmarsh in front being squeezed out entirely.

Conservation

Globally scarce and a UK conservation priority. Threatened by coastal squeeze, saltmarsh loss, development on estuary edges, and the difficulty of maintaining both nest banks and foraging marsh together.