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Foraging

Bees fly from the hive to collect nectars and pollens for food. Certain flower scents are especially attractive to foraging bees, and they particularly like blue and purple flowers. Indeed, a worker's two complex eyes, each with nearly 7,000 little lenses, are particularly sensitive to blue, purple and ultraviolet (UV) light. Nectar reflects UV light, and a worker detects this as a dark area in a flower. The other three of a worker's five eyes are simple eyes that sense polarized sunlight. Bees navigate by recognizing the landscape, and sensing the sun's position and the Earth's magnetic field.

A forager exhibits 'flower fidelity' by visiting only one type of flower per trip. Other bees in the colony may visit different types. Different nectars and pollens offer different proportions of their contents, encouraging a healthy diet.

Nectar

Nectar is a powerful attractant produced from sap by glands in a flower's nectaries. A hive's honey store is built up from many individual loads of nectar.

Honeybees have a short proboscis, so favour easily accessible nectar: for example, from flowers with a single ring of petals, multiple small flowers or a large trumpet.

Nectar is a watery solution of sugars, plus traces of acids, minerals, proteins, enzymes and various aromatic and other substances. Plants make sugars by photosynthesis. This involves converting water and carbon dioxide into oxygen and sugars using energy from light absorbed by the green plant pigment chlorophyll. Foragers prefer sweeter nectar because house-bees accept it more readily.

Nectar sugars vary in type and proportion according to a plant's species, and the soil, climate, weather and season. Sugars form 40-45 per cent of nectar by weight on average, but the proportion varies in different nectars. For example:

• Primrose

  5

• Plum

 15

• Apple

 25

• Lime

 35

• White clover

 40

• Kale

 50

• White horse-chestnut

 70

• Marjoram

 76

Nectar volume varies with flower species, soil moisture, air humidity and temperature, and rate of nectar flow. Nectar flow rises at certain times of day according to a flower's size and species. Temperature extremes can reduce or halt nectar production; warm weather increases it. Many wild flowers are excellent nectar producers.

This table (right) gives examples of the range of amounts of honey a colony of bees can make from 1 acre/2.5 hectares of land growing one type of plant:

Honeydew

Bees not only produce honey from nectar but also from honeydew, a sweet, dark or greenish liquid or crystalline substance excreted by aphids, leafhoppers and scale insects onto leaves or branches after eating sap. It's called honeydew because its droplets glisten like dew. Many honeys are made from both nectar and honeydew.

The manna referred to in the Bible was almost certainly honeydew.

Pollen

The nutrients in pollen include proteins (which strengthen bee-wing muscles), carbohydrate (which builds fat stores to provide energy for flying and warming the hive) and fats, vitamins, minerals and plant pigments (which promote general health).

Bees need pollens from a range of plants for optimal health. This is because the concentrations of nutrients vary in different plant species. Also, different plant pigments boost immunity in different ways.

Pollen can be yellow, orange, red, brown, black, green and even blue.

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