How many eyes does an insect have ?


Two? Yes some do, but in fact many insects have five. In addition to the multi-faceted compound eyes that are an obvious feature of larger insects, many also have an additional three simple eyes in the centre of the head, called ocelli.

If you find a dead bee in your garden have a good look at the head with a 10X hand lens or low power stereo microscope. The black beads between the compound eyes are the ocelli and can just be seen on the head.

The ocelli are simple structures and are believed they only detect light levels and movement. In contrast, the compound eyes are made up of a number of hexagonal facets which resembles a honeycomb and are capable of seeing much more. The number of facets effects the visual acuity and varies amongst different insect species. Lets take a closer look to the dragonfly’s thorax and head, it has a pair of large compound eyes which covered most of its head. Watching carefully, we can also see its pair of small antenna and three ocelli. Face is yellow with black marking on the labrum. There is the inversed ‘T’ marking on its frons. Its two large compound eyes are yellowish-green under the sunlight, touching with each others.

Dragonflies have very large eyes and have very good vision. Vision dominates their behaviour, including predation and looking for mates. The compound eye is made up of ommatidia which is a visual unit consisting of a lens system and a group of light-sensitive cells. A large dragonfly may have up to 30,000 ommatidia in each compound eye. Each ommatidium collects one visual information, together form a mosaic image in the dragonfly’s brain.

It is believed that the insects’ compound eyes are not as high-resolution as vertebrate eyes. However, the dragonfly’s visual system is extremely sensitive to movement and it points in almost all direction and gives the 360 degree visual field. There is the behavioural evidence that dragonflies have colour vision. Dragonfly eyes are also sensitive to polarized light.

The honeybee’s eye is estimated to have one per cent of the visual acuity of a human eye. Visual acuity (VA) is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain.

Below is a you tube video showing Insect Macro Photography. Hope you will enjoy it. Cheers !!!

Acknowledgment:

Dave Walker
http://www.brisbaneinsects.com

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About Deepak George Pazhayamadom

I'm a fish biologist and a mathematical modeller. I have a wide range of research interests, mostly centered on fisheries resource management.

Posted on May 29, 2010, in Biology. Bookmark the permalink. Leave a comment.

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