HAIRY HUNTER
ORNATE WANDERING SPIDER, BRAZIL
It seems that spiders don't like odd numbers. Two body segments, eight legs, one to four pairs of spinnerets and always an even number of eyes. Most spiders, like this ornate wandering spider, have eight simple eyes, but some have six or two. The way a spider catches its food has a strong influence on the ways these eyes are arranged. Web-building spiders, for example, tend to have smaller eyes that are evenly spaced apart, but the more centrally placed eyes of visual predators, like our friend here, are often enlarged. All the better to glimpse a tasty morsel with! There are principal eyes (the bottom pair here) and secondary eyes (the rest), which differ in structure and function. Principal eyes have sharp vision, along with retinas that can move behind their fixed lenses, helping the spider to track its prey. Meanwhile, the secondary eyes work together to provide a wider field of view, and identify objects and movements of interest.
SEEING RED
RED-EYED TREE FROG, COSTA RICA
The red-eyed tree frog likes to snooze the day away clinging to the underside of a tropical leaf. To stay undetected, they cover their lurid blue and yellow side stripes with their folded limbs, and tuck their bright orange feet under their bellies. A transparent lower eyelid, known as the nictitating membrane, creeps over the eye to camouflage it and keep it moist. If a hungry bird or snake approaches, the membrane lets in just enough light for the amphibian to become aware. Then it's show time! Eyes open, stripes out, orange feet 'in your face' - the frog does its best to dazzle the predator. It's a ballsy bluff, as this frog is neither poisonous nor combative. Its eyes are an evolutionary ruse to scare off predators. The hope is that the assailant will startle long enough for the frog to hop away.
この記事は BBC Science Focus の July 2022 版に掲載されています。
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この記事は BBC Science Focus の July 2022 版に掲載されています。
7 日間の Magzter GOLD 無料トライアルを開始して、何千もの厳選されたプレミアム ストーリー、9,000 以上の雑誌や新聞にアクセスしてください。
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