Cuckoo bees

How to recognise it

Mostly wasp-like: sparsely haired or nearly hairless, often boldly marked in red, yellow, black or white, with a hard shiny cuticle. Nomada species look convincingly like small wasps; Sphecodes are black with a blood-red abdomen. Crucially, females have no pollen-carrying apparatus at all — no leg brush, no abdominal scopa — because they never collect any.

• No pollen-carrying hairs on any part of the body. This is the diagnostic feature of the whole group, and it is visible with a hand lens.
• Sparse hair and a hard, often shiny and brightly patterned body — the armour of an animal that expects to be attacked in somebody else's nest.
• Seen flying low and slowly over bare ground or a nest aggregation, searching rather than foraging.
• Visits flowers only for its own nectar, never for pollen, so it is never seen carrying a load.

Body length 4–16 mm (typically 9 mm).

Biology

Social organisation

Cleptoparasitic — lays in other bees' nests

Builds no nest and gathers no pollen for her own young, laying instead in another bee's provisioned cell. Sometimes called cuckoo bees.

Nesting

Builds no nest

Builds nothing. The female's whole strategy is locating a host's nest at the right moment — after it has been provisioned and before it has been sealed — and depositing an egg. Some insert the egg into the cell wall so that it hatches after the cell is closed.

Carries pollen

Carries no pollen for young

On the wing

March to September

Each species flies when its host does, so the group as a whole spans the season while any one species is on the wing briefly.

Lifecycle

1. 1SearchingThe female patrols host nesting areas, often for hours, testing burrows. Her emergence is timed to the host's, which is why cuckoo bee flight periods track their hosts' so closely.Timed to the host species, typically a few weeks.
2. 2Egg layingShe lays in a provisioned host cell. In many genera the first-instar larva has enlarged sickle-shaped jaws used specifically to kill the host egg or larva, and then moults into an ordinary-looking grub once the competition is gone.
3. 3DevelopmentThe larva consumes the pollen store the host female collected, and overwinters and emerges on the host's schedule.One generation a year in most temperate species.

Where it lives and what it does

Habitat

Wherever their hosts are, which in practice means the same nesting banks, sandy paths and bee hotels. A cuckoo bee cannot exist anywhere its host does not.

Distribution

Worldwide, wherever host bees occur.

Behaviour

Unhurried and searching rather than purposeful. The characteristic sight is a Nomada flying slowly and repeatedly over a patch of bare ground, dropping into holes and coming out again. Because they need no pollen, they spend far less time at flowers than their hosts and are correspondingly harder to notice.

Pollination role

Negligible as pollinators. They visit flowers for their own fuel and carry no pollen deliberately, so incidental transfer is all they contribute. Their ecological importance is entirely different: as obligate specialists at the top of a bee food web, their presence indicates a host population large and stable enough to support a parasite, which is why surveys treat them as an indicator of habitat quality rather than as a problem to be solved.

Incidental only. This is the one bee group whose value is not pollination.

What it forages on

Visits flowers for nectar only, and is generally unfussy about which. Its real specialism is its host, not its forage.

Honey

Produces no honey

None, and the reason is worth stating: honey exists because a colony must survive a period without forage. A cuckoo bee has no colony, no nest and no stores of any kind.

Relationship with people

How people interact with it

Almost unknown to the public and routinely killed as wasps when noticed. There is no beekeeping relationship and no pest relationship — the group's only real interaction with people is through survey work.

Conservation

Cuckoo bees decline faster than their hosts and recover more slowly, because they need not just the host present but the host abundant. Several are among the most threatened bees in Europe for that reason. A site losing its cuckoo bees is usually a site whose host populations have already thinned, which makes them an early warning rather than a late symptom.