In common with most other insects the bumblebee compound eye is
formed of a large number of individual hexagonal units called ommatidia (above right).
The outside part that we can see is called the lens, this lies over the
crystalline cone, and beneath this are the visual cells leading to a nerve axon
and the brain. There are three types of visual cells, ultraviolet-sensitive,
blue-sensitive and green-sensitive. The ommatidia do not have any focusing ability.
Bumblebees, again in common with many other
insects, also have three ocelli (often called primitive eyes) arranged
in a triangular pattern on the top of the head, see the photographs above, below and on the right. Ocelli look like shiny bumps,
and resemble the 2 large "headlamp" type eyes easily seen in Lycosid spiders.
The ocelli detect changes in light intensity. In the photograph above of a Bombus lapidarius male only two of the
ocelli can be clearly seen as they reflect light. In the photographs below and below right all 3 ocelli can clearly be seen.
Bombus hortorum queen compound eyes and ocelli, note
the more elongated head typical of hortorum.
|The diagram on the right compares bumblebee vision and human vision.
The wavelength is in nanometres. So humans can see wavelengths from around 400
(blue) to as far as 800 (red) nanometres, whereas bumblebees can see from as
low as 300 (ultra violet) but only up as far as 700 (orange) nanometres.
The three basic colours seen by humans are red, green and blue, and by bumblebees they are green, blue and ultra violet. Bumblebees cannot see red, but they do visit red flowers. This is because as
well as being able to smell the nectar and any other attractive odour that the
flower may emit, many flowers, not only those we see as red, have ultra violet
patterns on the petals that are visible to bumblebees and some other insects,
but invisible to us.
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