‘On a warm, sunny April day a honeybee is attracted to a patch of bluebells. She – for almost all bees are female – is on a mission, and knows that she is close to her goal. She delicately clambers over the petals, as comfortable upside down as she is right way up, her legs working in unison. She pokes her head inside a trumpet-shaped bloom, searching for the sweet, sugary nectar.
‘Grasping the petal’s side, her legs force her head deep inside the flower, until her long tongue can get to the liquid. Once the tiny drop is all gone, she will move onto the next flower, and the next until she is full.’
A World Without Bees by Alison Benjamin and Brian McCallum
Almost every honeybee seen foraging on a flower in spring and summer is a female worker bee in the second half of her 30–35 day life. Having spent the first half inside the hive as a ‘house bee’ carrying out various tasks, she now spends her days as a ‘forager’ collecting four essential things for the colony: nectar, pollen, propolis and water.
What do bees forage for?
- Nectar: a mix of sugar, water and various ingredients collected from flowers in the forager’s honey stomach (yes, bees have two stomachs and one is just for honey!) and brought back to the hive to store as honey. Nectar is a valuable source of carbohydrate energy for bees.
- Pollen: dusted from flowers into ‘baskets’ on her hind legs, the forager brings back pollen loads to the hive where it is packed and stored in cells. Pollen is a source of protein, and also vitamins and trace minerals, for bees, who use it to feed larvae (brood food) and for young bees so that their bodies grow strong.
- Propolis: or ‘bee glue’ is a resinous substance collected from sticky buds or tree bark, and seen as shiny blobs on the third legs of foragers flying home. Propolis is used for sticking down small holes and insulating the hive, usually in late autumn in preparation for winter. It is also used for varnishing and hardening comb, such as the ‘propolis dance floor’ at the entrance where dances are performed. It is not stored and only collected when needed.
- Water: is needed to dilute honey stores (to eat) or to mix with brood food, and it is also used to cool the hive in high temperatures. It is not stored and only collected when needed. Foragers tend to collect water from unusual (dirty) sources such as hanging laundry, bird baths, puddles and drains.
Who forages what and when?
What foragers collect, and when, depend on the needs of the colony, the time of year and the temperature: for example, nectar flows, and can be collected, at 150C and above; propolis hardens, and can’t be collected, at 50C and under; and pollen collection may decrease if the queen slows or stops laying because it may not be needed for brood food.
Ted Hooper suggests that nectar, pollen, propolis or water may be collected by most foraging bees during their lifetime and that they usually carry one thing at a time, although nectar and pollen may sometimes be carried together and ‘some bees exclusively forage for propolis’ (Guide to Bees and Honey). Emily Heath writes in her module 6 revision notes that ‘two studies of bee collection habits found that about 58% of bees collect nectar only, 25% pollen only and 17% both nectar and pollen.’
Understanding the behaviour of the foraging bee
There is no doubt still a lot to learn about the behaviour of the foraging honeybee, although to summarise what we think we know is another beautiful infographic designed by Keith Whitlock for my blog. Click on the image to enlarge.
To really put into perspective the hard work of a foraging bee, here’s another excerpt from A World Without Bees.
‘The work demanded of the foraging honeybee is truly astounding. She will visit 1,500 flowers to collect just one load of pollen, which will weigh 15mg (1/1,900oz), about half as much as the nectar that she also brings back to the hive. To put these figures into some kind of perspective, it takes two million trips by a colony to collect the 30kg (66Ib) needed to raise its young, and four million trips to collect enough nectar to turn into honey for winter stores. This equates to around 45,000 trips per day per colony. Since a foraging flight may take a bee on a 10km (six-mile) round trip, collectively a colony can fly up to 450,000km (280,000 miles) a day. Each bee will fly around 800km (500 miles) in her lifetime, at times carrying loads equivalent to half her body weight; no wonder she will die of exhaustion about three weeks after her first flight.’
The figures of flowers visited, trips made and weights of loads all vary slightly from source to source and within different contexts such as nectar collectors vs nectar and pollen collectors, although all agree the bee is a master forager!
Are bees faithful to flowers?
The idea of ‘flower constancy’, meaning that bees become attached to foraging one type of flower for life, is a popular one and there are many theories to explain it – in another post! It may be an economic choice as by the time a forager learns a particular dance and becomes attached to a particular crop, she only has around 15 days to work it. Learning how to work different flowers might be a waste of time and energy. Ted Hooper says: ‘If, however, its [the bee’s] particular species of flower comes to an end in the first few days of the bee’s foraging, it will shift its allegiance to another plant, but should this happen towards the end of its life, it probably ceases to forage altogether.’
In the field, the forager prefers dense patches of foliage so she can move from one flower to the next with ease – an important fact to remember when planting for bees or planting for efficient pollination. ‘For instance, in orchards where the trees are planted in tight rows, with much bigger spaces between the rows than between the trees within the row, bees tend to work up and down the rows with very few crossing from one row to another,’ says Hooper. Similarly, the forager reserves her valuable glycogen stores for flying by walking from flower to flower if she can to collect nectar and pollen. ‘In dense forage such as clover or crucifers grown for seed, or dense stands of heather, bees tend to walk rather than fly from one group of flowers to another.’
How do foragers find their way around?
For a creature who is only 12mm long and weighs around 100mg, the honeybee’s body is remarkably well equipped to finding her way around.
- Two sets of eyes: a pair of compound eyes on the front of her head – each with 6,900 hexagonal lenses that interpret light (particularly sensitive to ultra violet light), colours and the position of the sun, and that have hairs to pick up wind speed and direction; and ocelli set out in a triangle on top of her head – light detectors that help to keep her the right way up.
- Two antennae: these ‘tune’ into smells to find flowers and her way around the local area and back to the hive.
And considering that a bee brain is no larger than a grain of sugar, the honeybee stores and communicates complex information such as location of the hive and various crops. A World Without Bees describes the honeybee’s impressive homing instinct.
‘A honeybee knows which nest to go home to by mapping out its locale. The accuracy of its measurements is quite uncanny, and when a number of hives are located near to each other with the entrances separated by a distance of only a few tens of centimetres the honeybee will return to its own colony, rather than the one next door.’
Having returned home from a successful foraging flight, the bee may perform various dances used to communicate good sources of forage as described in my previous post.
As a beekeeper, I love watching foraging honeybees in spring and summer as it brings home the magical alchemy of flower-to-bee-to-hive-to-honey-on-my-toast. I saw this forager on a clump of pink flowers in Regent’s Park last summer and filmed her with an extension tube on my camera as an experiment in macro video – it’s a little blurry. Enjoy!
Visit my blog index for more winter study posts.
Other links and further reading
Emily Heath has written two very interesting posts on bees and forage: 6th Honeybee behaviour revision post: bee foraging and “Bee foraging on garden plants: Sussex University research” – a talk by Professor Francis Ratnieks.
A recent article in Scientific American was brought to my attention by @andrewGouw on how bumblebees sense electric fields in flowers to guess where others have already fed on nectar. After following the link wait 15 seconds for the advert before the article appears.