It is amazing how a single question can open up a new world of knowledge.
When I photographed a couple of fly species pollinating sandalwood flowers, I noticed that the surface of their eyes had facets like gemstones, unlike the round shape of most insects. I caught house and March flies (an easy task this time of the year) and found the same. Why is this so?.
When I photographed a couple of fly species pollinating sandalwood flowers, I noticed that the surface of their eyes had facets like gemstones, unlike the round shape of most insects. I caught house and March flies (an easy task this time of the year) and found the same. Why is this so?.
 Type of blowfly |  Tachinid fly pollinating Frasers dryandra |
 Domestic house fly |  March or stable fly. Note spear like cutters around the proboscis |  Rhinidae fly |
I Googled insect vision and was blown away by a wealth of fascinating information that explains so much about insects and how they behave.
Lacewing reflected light hexagon from camera flash Our own eyes provide us with very clear coloured images with good depth perception and can detect fairly rapid changes of movement. We have two large movable eyes with lenses that can change shape and regulate light intake, and a sensitive retina that is backed up by large computing power.
Insects have compound eyes consisting of hundreds of single focus lenses that each have relatively few receptors (ommatidia). Most don't see very clearly but they are good at detecting movement. Ommatidia are packed together in a hexagonal, pentagonal or occasionally square array.
Upward facing pigmented eyes Most insects have a less comprehensive colour range than us and don't differentiate orange and red. However they can see ultraviolet colours that we can't. Many flowers have ultraviolet pigments that we can't see, but make patterns specifically designed to attract pollinators. Similarly insect eye colours act a sunglasses that filter out some colours and make their targets and predators more visible.
There are many tweaks that different insect have to adapt their vision to their lifestyle.
To get a full understanding please have a look at these fascinating blogs?
There are many tweaks that different insect have to adapt their vision to their lifestyle.
To get a full understanding please have a look at these fascinating blogs?
None of this explains why many flies have gemstone facet eyes. A possible link is that they are all fast flying insects that often interact with animals The facets enable more individual ommatidia to provide better focus in fewer directions that would enable them to react faster to say a swatting hand or tail. The slower flying insects below all have more rounded eyes.
 Bee flies |  Stiletto fly |  Soldier fly camouflaged eyes |
 Native bee |  Wasp |  Rhinotia suturalis weevils |
Dragonflies are an fast-flying exception but the following features greatly enhance their vision.
- Enormous eyes with more sensors per ommatidia.
- A huge range of colour receptors, and have the fastest movement detecting ability (flicker fusion frequency).
Have you ever caught a flying dragonfly?