Retinula Cells (Bug Eye Light Catchers)

Eyes made of many little eyes

Look closely at a photo of a fly or dragonfly. Its big eyes look bumpy, like a honeycomb. That is a compound eye. Each bump is the top of a tiny eye unit called an ommatidium.

Deep inside each unit is a bundle of about 8 long retinula cells. They stand side by side in a circle, like the slices of an orange.

Along the middle, each cell has a stack of tiny folds called a rhabdomere. That is where light gets caught.

Catching light

Retinula cells do the same job as the light-sensing cells in the back of your eye.

• Light comes in through the lens at the top.
• It shines down the middle of the bundle.
• The folds catch the light, and the cells send a message along nerves to the insect's brain.

Each unit sees one small dot of the world. The brain puts all the dots together into a picture. Compound eyes are great at spotting movement. That is why a fly is so hard to swat!

Retinula cell quiz