Squash bees

How to recognise it

Robust, honey-bee-sized and hairy, with a striped abdomen and dense pale hair. Males have notably long antennae, and both sexes have a slightly shaggier, blunter look than a honey bee. Females carry very large loose loads of the distinctive coarse, spiny squash pollen on the hind legs.

• Found in squash, pumpkin and courgette flowers, and effectively nowhere else.
• Active very early — often before sunrise, and largely finished by mid-morning when the flowers close.
• Males found asleep inside closed squash flowers later in the day. Nothing else does this.
• Carrying enormous, coarse, loosely packed pollen loads compared with a honey bee's neat wetted pellet.

Body length 11–16 mm (typically 13 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 vertical burrows in the ground, very frequently directly in the squash field itself, sometimes within a metre or two of the plants being pollinated. That habit is the group's biggest vulnerability: deep tillage destroys the nests of the pollinators the crop depends on, and a field ploughed conventionally each year loses its squash bee population.

Carries pollen

Scopa — dense hairs on the hind leg

On the wing

June to September

Lifecycle

1. 1EmergenceAdults emerge in midsummer, timed to the flowering of cucurbits rather than to the calendar — a single generation a year, tightly synchronised with one crop.June to July in most of North America.
2. 2Foraging and nestingFemales work the very early morning window while the flowers are open, provision cells with squash pollen, and are largely inactive by the afternoon.Four to six weeks.
3. 3OverwinteringThe larva develops on its squash pollen provision and overwinters underground, emerging the following summer as the crop flowers again.Roughly ten to eleven months.

Where it lives and what it does

Habitat

Squash and pumpkin fields, allotments, vegetable gardens, and the wild gourd populations of Mexico and the American southwest.

Distribution

The Americas only, from Mexico north into Canada and south into South America. Their historic range expansion northward tracks the spread of squash cultivation by Indigenous farmers over thousands of years, which makes them one of very few wild animals whose distribution was substantially shaped by pre-Columbian agriculture.

Behaviour

The timing is everything. Cucurbita flowers open before dawn and close in the heat of mid-morning, and squash bees have evolved onto that schedule — they are flying in near-darkness, finish early, and the males then sleep inside the closing flowers, sometimes several to a bloom. A gardener who looks into a closed courgette flower at midday and finds a bee in it has almost certainly found one of these.

Pollination role

Highly effective specialists. Cucurbita pollen is large, spiny and heavy and needs an insect that carries a lot of it; squash bees are built for exactly that plant and visit nothing else, so every grain they move goes somewhere useful. Multiple studies have found that where squash bee populations are healthy, they provide full pollination of a squash crop with no contribution from honey bees at all — which makes them one of the clearest cases in agriculture of a managed pollinator being unnecessary.

Very high on cucurbits and zero on everything else — the definition of a specialist.

What it forages on

Strictly oligolectic on Cucurbita — squash, pumpkin, courgette, marrow and wild gourds. Females will not provision cells with anything else, so a landscape without cucurbits has no squash bees regardless of how many other flowers it holds.

Honey

Produces no honey

None. Solitary, one pollen provision per cell, no colony to overwinter.

Relationship with people

How people interact with it

An unusually direct and unusually old relationship. Squash bees followed a human crop across a continent, and today they quietly pollinate a large share of the squash grown in North America while growers pay for honey bee hives that arrive after the flowers have shut.

Management

They cannot be bought or moved like mason bees, but they can be kept: reduced tillage, leaving field edges undug, and growing cucurbits in the same place year after year all favour a resident population.

Conservation

Not currently threatened as a group, but structurally exposed. A specialist tied to one crop is only as secure as that crop's cultivation and the soil it nests in, and deep annual tillage is directly destructive.