Small carpenter bees

How to recognise it

Small, 4-10 mm, with a nearly hairless, strongly shiny, often metallic blue-green or black body and a distinctly elongated shape. Many have a small pale mark on the face. They look far more like small wasps than like conventional bees.

• Small, shiny and near-hairless, often with a metallic blue or green sheen.
• Elongated, almost cylindrical body rather than the stocky build of most solitary bees.
• Seen entering the cut or broken end of a bramble or raspberry stem.
• A pale mark or stripe on the face in many species.

Body length 4–10 mm (typically 7 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

Hollow stems and plant cavities; Tunnels excavated in wood

Excavates a tunnel down the soft pith of a broken or cut stem — bramble, raspberry, elder, rose, sumac and the dead stems of large herbaceous plants. The female chews out the pith, provisions a linear series of cells separated by pith partitions, and then remains in the nest guarding the entrance. Nests require a stem that has been cut or snapped, which is why the genus depends so directly on how gardens and verges are managed.

Carries pollen

Scopa — dense hairs on the hind leg

On the wing

April to September

Lifecycle

1. 1Overwintering as an adultUnusually, Ceratina overwinter as adults inside a stem rather than as a prepupa, often with siblings, and emerge in spring already mature.Autumn to spring, inside the natal or a new stem.
2. 2Nest founding and provisioningThe female excavates a stem and provisions a linear series of cells through late spring and summer.Several weeks.
3. 3Maternal careShe stays at the nest entrance guarding it against parasites and predators, and in many species she is still alive when the offspring mature — feeding them, cleaning the nest and in some cases releasing them. Sustained maternal care of this kind is rare in solitary bees and is exactly the behaviour from which eusociality is thought to have arisen.

Where it lives and what it does

Habitat

Anywhere with cut or broken pithy stems — gardens, hedgerows, brownfield land, woodland edge, scrub and roadside verges.

Distribution

Worldwide except Antarctica, and abundant across Europe, Asia, Africa and the Americas.

Behaviour

Quick, inconspicuous and generally overlooked. The genus is scientifically important out of proportion to its profile because of the maternal care: guarding a nest and interacting with adult offspring is a behavioural bridge between the solitary majority of bees and the eusocial minority, and Ceratina is one of the best-studied examples of it.

Pollination role

Useful generalist pollinators, particularly of small-flowered plants that larger bees find uneconomic. Their abundance makes them collectively significant even though no individual carries much pollen.

Moderate per individual and meaningful in aggregate through sheer numbers.

What it forages on

Broad generalists on small open flowers — composites, umbellifers, brambles and mints.

Honey

Produces no honey

None. One pollen provision per cell, in a stem.

Relationship with people

How people interact with it

Almost entirely unnoticed, and directly affected by an extremely common gardening decision: whether dead stems are cut to the ground in autumn or left standing. Few insects depend so precisely on a habit most people never think about.

Conservation

Not globally threatened, and locally reduced wherever verges and gardens are cut to the ground each autumn. The habitat requirement is unusually cheap to supply and unusually easy to destroy.