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April 2007



Honeybees' Yellow rain means free fertilizer

By Dr Garth Cambray

To many people, those little yellow dots that appear on vehicle windows are a mystery. But to many of us they are something that helps us eat every day. The yellow dots are bee dung. This article will show you how bee dung is an important part of your food chain.

Honeybees can fly up to six kilometers from their hives. They visit flowers and collect pollen and nectar which they take back to the hive. This pollen and nectar is then processed by bees in the hive into food. After digesting pollen, food manufacturing bees need to excrete the indigestible matter that is left over this takes the form of all the pollen granules with their nutritious inner sections removed. To 'go to the toilet', bees fly out of the hive and release the pollen remains as a few drops of yellow (normally) liquid. If the bees have upset stomachs then this will be more of a squirt than a drop, but either way if it lands on your window you will see it as a sort of yellow splat.

The bees normally use an area within a radius of 20-30 meters of the beehive as a toilet zone. It has been estimated that an average beehive produces as much as 45kg of bee dung per year, which is all, neatly deposited around the beehive as a high nitrogen manure. When it rains, this pollen dung washes into the soil, breaks down and provides an excellent natural fertilizer. Hence, to a farmer, who brings bees into a field to pollinate a crop, they may get more fertilization than they realized.

To use an example, in the western cape region of South Africa, many beekeepers pollinate apple crops. The apples are grown in small orchards in narrow valleys bees are brought in to the crops in spring when the honeybush, a legume, which grows in the hills nearby, is flowering. In many cases, the bees fly to the apple flowers early in the morning, pollinating them, but later in the day, fly out into the hills and harvest pollen and nectar from the honey bushes in the mountains. When they 'go to the toilet', these bees deposit relatively large quantities of nitrogen rich pollen dung in the apple growing region.

In ancient agricultural countries such as India, the value of bees to farmers is well understood. In many areas teak and fig trees are planted near fields to attract the tree nesting Apis dorsata, giant bees which build open nests hanging from branches. In some fields trees with 20-30 beehives is not uncommon. To the farmer these bees represent in excess of 800-1200kg of high nitrogen manure spread evenly over the fields per year. This nitrogen is all harvested from surrounding areas and deposited in the fields for free.

DIY guide to bee manure

So, for farming in Africa, how do we use bees to fertilize our fields with free nitrogen rich manure? Here's how you would go about doing it. 

For small fields, design the fields so that beehives can be placed in the middle of a circle of fields, with enough space around the hives that they won't hamper field work. If a circle of plants, such as bamboo or cane is planted around the apiary, it will stop the bees being able to see field workers and will reduce the risk of stingings. Given that bees go to the toilet within a range of 10-40 meters of the hive, it means that a farmer can have a patch of field with 4 apiaries placed in a cross shape in that field.

In this diagram, apiaries represented by a small square have slightly overlapping toilet zones. This radius of the circles is 40m, giving an area of just short of 2 hectares fertilized with bee manure.

The toilet zones of each apiary will overlap and thus the field of about 2 hectares will receive the distributed excretia of the beehives. If each apiary has 10 beehives, this would mean that the field would receive a total of 1.8 tons per year of manure from the hives. Assuming a rough content of 16% nitrogen this would equate to nitrogen fertilization of 144kg/hectare way in excess of the amount required in added fertilizer in normal maize farming.

In this way, careful placing of beehives, in addition to providing a living from honey and wax, also provides a source of cheap nitrogen fertilizer for the small scale farmer. In areas such as the north of Zambia where leaching of the soil results in field collapse rapidly, careful spacing of beehives can provide a means to sustainable utilize small pieces of land for food production.

More information:

  During the Vietnam war, legend has it, rookie US soldiers were taken to stand near trees with beehives in rice paddies at sunset when the bees fly ' to the toilet'. Soldiers were told to stand, staring at the sky and to watch what happened. Around large trees with more than 100 beehives in them, this would be a case of soldiers watching in awe as the sky went brown with bees above them, and then suddenly watching in disgust as they turned yellow with dung, much to the joy of the commanding officers standing a little further back. Later, this concept of yellow rain was copied with the far more sinister manmade agent orange rain which killed off many of the forests of Vietnam, and many of the bees as well thus breaking the important cycle of bees carting nitrogen to fields from forests.

Dr Garth Cambray is a beekeeper and scientist based at Makana Meadery in South Africa.

Related articles:

The all important Bees in the Biodiesel equation

 African bees a solution to North America's bee problems?


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