The senses bees have and we do not

Electric fields

A flower connected to the ground carries a small negative charge. A bee in flight picks up a positive charge from friction with the air. The difference produces a weak electric field around the flower, and its shape changes for a while after a visit, because the departing bee leaves the flower slightly less negative.

Bumblebees learn to associate field patterns with reward, and discriminate flowers by field alone when colour and scent are held constant. The receptor appears to be mechanical: fine body hairs are deflected by the field, and the deflection is transduced by the same kind of mechanoreceptor that detects touch and air movement. An effect that sounded exotic acquired a plausible mechanism within three years, which is unusually quick.

Polarised skylight

The dorsal rim of each compound eye contains receptors arranged to detect the polarisation of scattered sunlight. Because that pattern radiates around the sun's position, a bee that can see a patch of blue sky can infer where the sun is even when the sun itself is hidden. It is the basis of the sun compass, and it is what allows the waggle dance to encode a solar bearing on an overcast day.

Vibration, air movement and sound

Bees have no ears in the usual sense. Johnston's organ, in the second antennal segment, detects the movement of air particles and vibration transmitted through a surface. That is how a follower reads a waggle dance in a completely dark hive: she is detecting the dancer's vibrations through the comb and the air jets from her wings, not listening to a sound.

The same channel carries the stop signal, the shaking signal and queen piping, all of which are vibratory messages delivered by contact or through the comb. A bee colony is, in acoustic terms, a network in a solid rather than in air.

Humidity, temperature and carbon dioxide

• Antennal hygroreceptors detect humidity, and the brood nest is held within a narrow band because egg survival depends on it.
• Thermoreceptors detect temperature, and the brood nest is held close to thirty-five degrees Celsius — the tightest thermal regulation of any insect nest.
• Carbon dioxide sensitivity triggers fanning, so an individual threshold produces a collective ventilation system with no one coordinating it.
• A circadian clock supports time-of-day memory: bees learn when a flower species secretes nectar and turn up then.

Magnetism, and the honest state of it

Bees change their behaviour in altered magnetic fields. Comb-building orientation, homing and trained discrimination tasks have all shown effects, reported repeatedly since the 1970s. Magnetite-containing structures have been described in the abdomen and proposed as the receptor.