 WETlandsa publication of Sungei Buloh Nature Park |
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7 No 2 Aug 2000 The Truth about Grass Butterfly-Plant Relationships List of butterflies (1999-2000) Beauty to Behold how animals see More about the eyes of animals Nesting Birds at Sungei Buloh Nesting Little Heron A walk with a Volunteer Guide: Keith Hillier Nature Photographer with a Mission: Julian Wong Earth Day Programmes Nature in the City |
 Spider
Spiders normally have eight eyes, but some spiders have six, four or two
eyes. One unusual species has only one eye, which is in fact, a fusion of
a pair of eyes. Ironically, the majority of spiders do not depend on their
eyesight for finding and capturing prey. They have extremely poor eyesight. Prawn
Most crustacea have compound eyes. A compound eye is made up of separate
compartments and the animal's brain can put the images together to form
a complete picture. Prawns can detect movements in water using their two
large eyes.
Dragonfly The dragonfly has
a pair of eyes that cover most of its head. There are up to 30,000 lenses
in one single eye and these lenses can detect objects up to 20 metres away! Lizard
Lizards in general have good eyesight. Colour is important to lizards such
as the Changeable Lizard as they communicate using their colourful head
ornaments, crest and throat. It is also a way of distinguishing between
the sexes. The eyes of most reptiles are large and well developed. Their
eyeballs and lenses are usually round. Pupils range from round to elliptical,
usually vertical and occasionally horizontal. The eyes are protected by
transparent solid lenses. They have moveable eyelids and some can close
their eyelids to tiny peepholes! Fish
Unlike humans, sight is not as important to fishes as most can navigate,
detect obstacles and locate food in murky water through vibrations received
from their lateral line system. The lateral line system is made up of tiny
perforations in a single row of scales and runs horizontally along the length
of the fish. They are adapted to these conditions and in fact see most clearly
in dim light! The Archer Fish is an exception and it has better eyesight
than most fishes. It needs to look through and above water for insects that
it feeds on. Most fishes have a clear layer of skin protecting their eyes,
as they do not have any eyelids. More about the Archer
Fish. Bird
Most birds have keen eyesight and their eyes can be as heavy as their brain.
Birds are sensitive to visible and polarised or filtered light. Although
filtered light is undetectable, sunlight reflected from some parts of the
sky is partially polarised. Experiments have shown that birds use this polarised
light to navigate after sunset, before the stars shine brightly. Bat
"Blind as a bat" is a wrong term to use as there as no known species
of blind bats! Some species have better eyesight than others, some have
bigger or smaller eye size, and some can or cannot see colours. In general,
a bat takes full advantage of available light by increasing the light density,
using a reflective structure called "tapetum lucidum" located
behind the retina. For more about bats. Mudskipper
Unlike other fishes, the mudskipper has a pair of closely located, bulging
eyes above its head. It can see above and below water at the same time when
it swims, just like a periscope of a submarine. Being a fish that spends
much of its time above water, seeing "double" is essential for
its survival. It can spot predators from above and under water simultaneously.
For more about mudskippers. |
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