Sweat bees

How to recognise it

Mostly small and slender, from 3 to 10 mm. Many are dull black or brown with pale hair bands across the abdomen; a substantial number, particularly in the Americas, are a brilliant metallic green or blue-green that looks nothing like a conventional bee. Females carry pollen on the hind legs.

• Small — often much smaller than a honey bee, and easy to mistake for a fly at a glance.
• A metallic green or blue-green body rules out almost everything else; no European honey bee, bumblebee or wasp is metallic.
• Attracted to perspiration on hot days, landing on skin to drink salt and moisture. Almost no other bee does this.
• Females of many species carry a visible pale band of hair across each abdominal segment.

Body length 3–10 mm (typically 6 mm).

Biology

Social organisation

Primitively eusocial

Social behaviour without the sharp physical caste separation of honey bees — the queen looks much like her workers. Some sweat bees.

Colony size at peak

2–200 individuals

Colony lifespan

One season, in the species that are social at all.

Winter

Mated females overwinter alone in the nest burrow or in soil, and found or refound a nest in spring. There is no overwintering colony and no stored food to survive on.

Castes

Foundress or queen, Workers, often barely distinguishable from her

Nesting

Burrows in the ground; Tunnels excavated in wood

Most dig burrows in bare or sparsely vegetated soil, often in aggregations of many separate nests packed into a favourable bank or path. A minority nest in rotten wood. In the social species several females share a single burrow system with one reproducing and the rest foraging, which is a colony in function while looking almost nothing like a hive.

Carries pollen

Scopa — dense hairs on the hind leg

On the wing

March to October

A long season, with different species peaking at different points. Some are among the last bees flying in autumn.

Lifecycle

1. 1Spring foundationAn overwintered mated female emerges, digs or reoccupies a burrow, and provisions the first cells alone.March to May in temperate regions.
2. 2First broodIn social species the first brood emerges as small workers that stay and forage for their mother rather than founding their own nests. In solitary populations of the very same species, they leave and nest independently.Six to eight weeks from egg to adult.
3. 3Reproductive brood and overwinteringA later brood produces males and new females. The females mate, the males and the old foundress die, and the mated females overwinter to start again.Late summer into autumn.

Where it lives and what it does

Habitat

Almost everything: gardens, meadows, farmland margins, brownfield sites, sand dunes, woodland rides and deserts. The binding requirement is bare or thinly vegetated soil to dig in, within reach of flowers.

Distribution

Worldwide except Antarctica, and unusually well represented at high latitudes and altitudes as well as in the tropics.

Behaviour

Quick, low and unobtrusive foragers that work small flowers a honey bee would ignore. Many are generalists, which is part of why they matter agriculturally — they are already present and already visiting when a crop opens, rather than needing to be brought in. The attraction to perspiration is a genuine mineral-seeking behaviour rather than a nuisance habit: salt is scarce and bees need sodium.

Pollination role

Collectively among the most significant wild pollinators in the world, precisely because they are abundant, widespread, generalist and active over a long season. Studies of crop pollination that separate wild bees from managed ones repeatedly find halictids doing a substantial share of the work, and doing it in conditions and at times honey bees are not flying.

High in aggregate through abundance and season length rather than through per-visit efficiency; individually they carry less pollen than a mason bee or a bumblebee.

What it forages on

Mostly generalists, with a scattering of specialists on particular families. Their small size lets them work small, shallow flowers that larger bees find uneconomic.

Honey

Produces no honey

None. Even the social species store only what the current brood will eat, because the colony does not survive the winter — there is nothing to store for.

Relationship with people

How people interact with it

Almost entirely unnoticed, except on hot days when they land on people. They are the clearest illustration available of how much pollination happens without anyone managing it.

Conservation

Individual species are declining with the loss of bare ground and flower-rich margins, though the family as a whole is not threatened. Sweat bees are heavily affected by soil sealing — tarmac, paving and dense turf all remove nesting habitat that looks like nothing to a human eye.