European Hornet (Vespa crabro) head showing the three ocelli positioned between the two compound eyes.
Ocelli (singular Ocellus) are simple photo-receptors (light detecting organs). They consist of a single lens and several sensory cells. Unlike compound eyes, ocelli do not form a complex image of the environment but are used to detect movement. Most arthropods possess ocelli.
Taken on my bug hunt today, I have been searching all year for a hornets nest and now at the end of the season I found one. I saw Many hornets hunting up and down a hedgerow so I followed them in one direction and tried to see if they were heading home and luckily they were I found a nest in a old willow tree.