Eyes
Margaret Thomas NDB

info@scientificbeekeeping.co.uk

Diagrams redrawn by Jackie Elliott

This information is based on an article that appeared in the Scottish Beekeeper Magazine in May 2017

The three simple eyes are called ocelli. These eyes have a lens and numerous sense cells. The focal point of the lens is much beyond the outer ends of these retinal cells. The dark pigment in the retinal cells moves from the base to outer ends of the cells in response to light. This is why it is thought these eyes only act as light sensors, useful when flying to indicate where the sky is. This is probably why bees get confused flying over water, turning over when light reflects off the waters' surface.


The two compound eyes are made up of many smaller units called ommatidia, placed in an arc either side of the bee's head. The number of ommatidia vary between the casts and the sexes, the queen having the smallest number, around 3,500, the worker 5-6,000, and the drone around 10,000 (Goodman). Each ommatidia is six sided and edged by pigment cells, which stop light spilling over from one unit to the other. Each ommatidia is an elongated structure, a lens at the outer surface, 4 crystaline cones, then light sensitive slender structures, eight or nine of these making up the retinula. In the centre where the eight (or nine) cells meet they form a rod like structure called the rhabdom. This area is thought to direct light into the retinula cells. The retinula cells end in a nerve fibre going directly into the optic lobe of the brain. Each retinula cells is sensitive to a different colour. Bees see colour very similarly to how we see it, but the range is from yellow to ultra violet through blue green and violet. Red is perceived as black. Ultra violet is particularly pertinent to bees as many flowers have ultra violet markers pointing to the nectaries. Detecting polarised light is also a bee skill. Being able to visualise the plane of polarisation is a necessary navigation skill when the sky is cloudy.

Image 2 : Ommatidia

Image 1: Anterior view of head showing position of Ocelli in three different types of Bee

Bees have five eyes. Three are simple eyes located on the top of the head on the queens and workers, but pushed forward onto the forehead on drones. The other two eyes are compound eyes located either side of the head. The reason the drones simple eyes are pushed forward is because his compound eyes are much larger and meet in the centre of the head.

Having so many individual 'eyes' allows the bee to see movement, useful to observe and focus on moving flowers. This ability is measured by 'flicker frequency'. This is about 300 per second and six times greater than humans can perceive movement. The bee perceives the word in a mosaic pattern.
However these eyes have poor visual acuity compared to ours. Their vision being 100 times less acute than ours. The individual ommatidia do vary in size so central vision is probably more acute. Maybe they see what I see trying to read without my glasses!

Further reading in Morse and Hooper Illustrated Encyclopedia of Beekeeping, Goodman Form and Function of the Honey Bee