The most obvious spiders you see at night are various wolf spiders in the family Lycosidae. Wolf spiders are one of the few groups that have good vision and hunt prey and court one another by sight.

They have bigger eyes, particularly the four at the front, which they need because they are often active at night in limited light and the larger eyes receive more light and concentrate it just like other nocturnal animals that use sight. The wolf spider's side eyes are good for picking up movement where the spider isn't actually focussing on at the time.

Their eyes, which are adapted to the night, reflect brightly in torchlight. Interestingly some huntsman spiders have a slightly less reflective eyeshine with a distinctly greenish tinge.

Wolf spiders are unlike most other spiders which have poor vision and rely on touch and air movement to find prey and dodge predators. Although most species have eight eyes, their vision isn't as acute, and is mainly used to detect shadows passing over them. It's enough to signal danger, and to tell them which direction light is coming from so they can hide in the dark.

The number of eyes is variable across the order. Some have eight, and some have only six. Some even have no functional eyes at all.

If you've shone a torch on animals at night, you will often see the glow of their tapetum lucidum. This is a layer in the eye that reflects light back onto the retina, which greatly enhances their vision in the dark. Cats and rabbits have this, but humans don't. This is why our night vision is so bad by comparison. It's also why our eyeshine is dim and tinged red by blood.

An amazing variation is the net-casting spider Deinopis, which has two huge rear eyes. This gives them the frightening name of "ogre-faced spiders". They are specialised for low-light night vision, with an enormous field of view and ability to collect light.

The price they pay is that each dawn, their light sensitive membrane is destroyed and has to be manufactured again that night. The benefit is it enables them to accurately track and catch their prey at night.

They place white faecal spots on a leaf below the net, which they use for aiming points. Interestingly, they do this without the help of a tapetum lucidum which other spiders have.

Response by: Martyn Robinson, Naturalist

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