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#4: Simple Eyes




Litinsects #4: Simple Eyes

 Yesterday I talked about compound eyes, the multi-faceted structures that most insects use to see the world 👀 But insects actually have another visual system as well, composed of simple eyes or OCELLI. Unlike compound eyes, ocelli are composed of only one structure which makes them comparatively “simple” although they are still very important. These are light-detecting organs consisting of a single lens with sensory cells. They can detect movement but don’t form complex images.

  • “Ocellus” comes from the Latin word oculus, meaning eye. So these structures are literally “little eyes”
  • Ocelli are located on the insect’s head, usually between or adjacent to the compound eyes. They are usually dome-shaped, somewhat shiny structures
  • In most flying insects (such as flies, dragonflies, bees, etc.) there tend to be three ocelli in a triangle arrangement (see photo). Some terrestrial insects (like cockroaches) have only two ocelli
  • All adult insects with compound eyes also possess ocelli (except it really isn’t all, there are always exceptions 😉). So insects actually see using two distinct visual pathways with anatomically independent structures
  • Some types of arthropods have only simple eyes. For example, spiders have multiple pairs of simple eyes arranged around their heads. Millipedes and centipedes also have simple eyes in most cases
***Now for a little test, go back to my post from yesterday and see if you can find the ocelli on that fly!***
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