All eyes on invertebrates
The eyes of invertebrates come in a spectacular range of shapes, colours and forms – they are very different than our own. Some minibeasts have excellent vision, and for others it is extremely poor, but it is safe to say that none of them see the world in quite the same way we do. Their eyes, however, are all perfectly adapted for their way of life. Whether it be on the wing or crawling through an underground burrow, minibeasts have ways of getting by – and many have remarkable visual abilities.
Insects have ‘compound’ eyes. Their eyes are made up of many tiny lenses, all combining to form an image. Some dragonflies have 29,000 individual lenses in their eyes and can see 360 degrees. It is quite a mind boggling thought from our point of view - imagine trying to cope with seeing everything at once! Nevertheless, dragonflies do it, and it allows them to fly with incredible precision and to catch other insects as they zoom through pond reeds at breakneck speeds.
A dragonfly eye close-up revealing the myiad of compound lenses - some magnified by the water droplets.
The eyes of praying mantids are also compound eyes, but are arranged in such a way as to allow them to strike accurately to catch their prey. They too have vision which wraps right around them, but not quite as wide as the dragonflies. Mantids and many other insects have obvious ‘pseudo-pupils’ – a black dot in the eye. This dot is called a pseudo-pupil and appears to change position depending on where you view it from. this is an optical illusion which creates the impression the mantis is always watching you. This is a handy thing to have as predators sneaking up will think they’ve been spotted.
Spiders have very different eyes than insects. They have single lens eyes, rather than the compound eyes with most spiders having eight of these single eyes. Many spiders have tiny eyes and relatively poor eyesight, relying on their other senses, but some species have great eyesight. Jumping spiders and wolf spiders are two groups which have noticeably large eyes, and can see very well. Both these groups of spiders have their eyes spread right around their head, so like many insects, they too can see what is going on behind them.
Snails eyes are even a little more bizarre. Although their eyesight isn’t great, it is good enough to allow them to find their way around. The remarkable part about their eyes is that they can retract them by turning them inside out - their eye-stalks (tentacles) actually invert when they are withdrawn, just like a rubber glove being pulled back inside itself.
