Why Do Bees Have 5 Eyes?

Bees have:

  • 2 compound eyes - these are the obvious eyes at the sides of the head;
  • 3 simple eyes know as ocellus or ocelli.  These small eyes are less conspicuous than the compound eyes, and are arranged in a triangle on the top of the head between the compound eyes.   If you look very carefully on the image above, you can just make out at least one of the ocelli (the one at the front) as a shiny round black dot.

It should be noted, however, that bees are not alone in the insect world for having 5 eyes, and specifically for having 3 ocelli on the top of the head: dragonflies, wasps, and grasshoppers also have them, among others. 

Compound eyes - what are they for?

The compound eyes on bees are clearly visible at the sides of the head.Above: The compound eyes are clearly visible at the sides of the head.

In bees, each compound eye is located at the side of the head (in contrast with true flies, for example, which have the two compound facing toward the front).

With hoverflies, note how the large eyes are forward facing.Above: This is a hoverfly. Note how the large eyes are forward facing.

Each eye comprises thousands of individual lenses.  They pick up the immediate environment, color and shapes.  These eyes enable bees to see UV markers in the flowers that guide the bee onto the 'landing platform' of the flower, and to the nectar reward. 

Each tiny lens of the compound eye perceives the surroundings from a very slightly different angle.  The sum total of these images recorded by the many lenses, provide the overall picture of the bee's surroundings.

What are the ocelli for?

The ocelli are also called 'simple eyes', because each eye has just one lens, but with many sensory cells.

These simple eyes do not form an image of their immediate environment as the compound eyes do.  They are used by bees for orientation and navigation according to the position of the sun. 

Interestingly, bees that fly at dusk or dawn have larger ocelli in order that they can pick up on the reduced sunlight when the sun is low in the sky.  You can read more about this on my page do bees fly at night.

Facts about bee vision

Bumble bee visiting Escallonia.Above: Bumble bee visiting Escallonia -"Red claws".
  • It is believed that bees are near-sighted, due to each of the lenses in the compound eyes being so tiny, meaning that each lens only sees a tiny amount of the world around it.

  • Bees may be near-sighted, but they process images 15 times more quickly than humans do.  This means, for example, that what might appear to be an even fluorescent light to us may well appear as a flickering light to a bee.

  • Bees can recognise most colors perceived by humans, but they do not distinguish red very well.  However, they may visit red flowers because they are able to perceive the ultra-violet markings inside the flower that we humans cannot see.
Bees may not pick up on red hues, but may still visit red flowers.  It is believed that bees can see ultra-violet markings in the petal that indicate rewards for the bee!Above: Bees may not pick up on red hues, but may still visit red flowers. It is believed that bees can see ultra-violet markings in the petal that indicate rewards for the bee!
  • Bee eyes are most attuned to see green, blue, and ultra-violet light.

  • Black is not the only eye color for bees.  There are bees with different colored eyes - even blue, such as the digger bee - Melissodes stearnsi and the Blue eyed Carpenter Bee Xylocopa tabaniformis parkinsoniae
    Some bees even have large, green eyes.  This can be seen on a number of species such as some
    Anthophora, Xylocopa, Halictid
    species among others.  Below is a Megachilid - this silvery leafcutter bee male below has pale green eyes:
Above: The eyes of the male silvery leafcutter bee are an interesting shade of pale green.
  • Honey bees have hairy eyes!  It should be noted that this is not true for all bee species!  A study by Georgia Tech found that the honey bee can carry up to 30 percent of its body weight in pollen because of the very clever use of hairs covering the entire body (in various densities) - including the eyes!  

    The research found that the gap between each eye hair is approximately the same size as a grain of dandelion pollen, which is typically collected by bees. This keeps the pollen suspended above the eye and allows the forelegs to comb through and collect the particles when grooming.  Watch this very short video below - part of it is slowed down so that you can observe the clever honey bee in action.  The scientists observed that honey bees were able to groom 15,000 particles of pollen in 3 minutes(1)!




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References

(1) https://www.news.gatech.edu/2017/03/28/hair-spacing-keeps-honeybees-clean-during-pollination










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