The Head

Compound Eyes

Unlike humans who have a single lens, insects have compound eyes made up of thousands of hexagonal lenses.

 

Ommatidia: the structural components of the compound eye

Note that vision is different in insects than for us. Each lens of the compound eye sits on top of an ommatidium (plural ommatidia). Each ommatidium sends a signal along a nerve with information about what it sees to the base of the eye where the signals gather together to form the optic nerve (a bundle of nerves with contributions from each ommatidium). The group of images are then integrated in the brain for interpretation of what the insect is seeing.

Because many insects have eyes that wrap all the way around their head, such as dragonflies, some insects can see in front, to the sides, and behind them at the same time. This comes in handy for catching prey while flying through the air.

This video depicts what a bee sees as it flies among flowers foraging for nectar and pollen. Note the image of the insect eye with separate lenses (hexagon shaped) of the ommatidia as it detects the color patterns in the field of flowers. Then as a bee feeds on nectar in a flower, note how the curved stamens of the flower (stalk containing pollen at the end) tilt down when the bee steps on the petals, brushing pollen onto the bees’ back.

The Strange and Unusual Tale of the Four-eyed Whirligig Beetle

These surface dwelling aquatic beetles have one of the most unusual visual modifications of any insect.

Click the play button to watch the animation below (be sure the volume is up on your computer.)

 

For an alternative version of the Flash movie above, download the PDF file, Whirligig.

The Whirligig brings up an important point about ALL variation in insects

• Variability in traits exist in all populations of organisms through mutation and genetic recombination
• Some variation in traits allow organisms to survive better in changing environments
• These variations = adaptations
• This process is involved in evolution; a topic we will cover in more detail later. But it has been through the process of evolution that insect species became so diverse and numerous.

Simple Eyes: Ocelli

Simple eyes, or ocelli, are alternate light sensing organs (arrows point to ocelli). The ocelli do NOT make pictures, but sense light and dark.  This is especially important for insects that live inside a tree, in soil, or inside a plant. These sense organs allow insects to “know” when days are getting longer or shorter. This can be critical for timing emergence from their overwintering site to find their food source growing at the right time, and finding suitable mates.

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