Six ways animals use fake eyes
Eyes can be beautiful. Mysterious. Alluring. They can also be deceptive, no more so than in the animal kingdom, where a range of species display fake eyes on their bodies.
Such eyespots, which appear on fish, frogs, butterflies and birds and insects among others, have fascinated natural historians for centuries, and a fresh look at the science of eyespots reveals some modern surprises.
Plenty of species appear to use eyespots as a warning signal to predators, helping to deter, prevent or delay their attacks. That could be due to the unfamiliarity of the shape to predators, or because eyespots fool predators into thinking they are staring at the face of an even bigger, more dangerous creature than themselves.
But few had checked rigorously unbiased by our own human perception of these markings as until Dr John Skelhorn at Newcastle University, UK examined how birds responded to a series of fake caterpillars with snake eyes.
Lots of caterpillar species sport eyespots, so Dr Skelhorn team created plump, realistic caterpillars from edible pastry, then painted them with eyespots on different parts of their body. They reasoned that birds would reject caterpillars that sported eyespots at their fronts, where an eye would normally be, thinking the insect was actually a snake. best fake id sites But they wouldn be deterred by caterpillars with eyespots elsewhere.
Their research supported their hypothesis; birds were more reluctant to attack caterpillars that had eyespots in the right place to mimic a snake head.
View image of Pairs of eyes, or a just a shocking pattern? (credit: Robert Pittman CC by 2.0)
Butterflies that flutter their eyes
But other studies have shown the opposite; that butterflies use eyespots as conspicuous, disorientating patterns that put off predators, rather than to mimic the eyes of other animals.
Eyespots are also surprisingly common on butterfly wings, for example. Yet they vary in size and brightness, and it was unclear why.
To investigate, Dr Martin Stevens at the University of Exeter, UK examined how birds actually see butterflies, which they often like to eat. idemperor.com
Affixing fake butterflies to tree trunks, Stevens team presented wild woodland birds with spots of different shapes, sizes, and contrasts, in order to manipulate the level of eye likeness. They predicted that if eye mimicry is important, birds should be more wary of spots with a black centre and white surround, compared with the inverse arrangement. They found that the two patterns were equally avoided.
Eyespots have attracted a substantial amount of experimental work but there still a great deal left to understand about them
Retaining the size of the colour pattern on the fake butterflies, they changed the shape from circular to rectangular, and again didn’t find any difference in birds avoidance. Contrast did matter though. When test patterns had higher contrast against the background, those areas of the fake wing were more likely to be avoided.
The results suggest that it is conspicuousness, not necessarily eye mimicry, that matters.
don have the complete picture yet, says Stevens.
His experiments were with fake, stationary butterflies, and the spots and contrast patterns were continuously visible. In nature, butterflies and moths often flash open their wings to reveal their eyespots, no one has done an experiment yet doing these kind of manipulations with a startle display, he says. idpurchase.com But his work thus far suggests that birds will avoid conspicuous patterns when they are bigger and more contrasting, whereas shape doesn’t seem to matter.
have attracted a substantial amount of experimental work but there still a great deal left to understand about them, and why they so diverse, says Stevens.
View image of Physalaemus frogs have a deceptive rear end (credit: Photoshot Holdings Ltd / Alamy)
The frog with a toxic look
As well as sporting large eyes, some animals can inflate their eyespots, in a bid to stare down, and intimidate their enemies.
One frog that inhabits the savannah of Brazil, called either Physalaemus nattereri or Eupemphix nattereri, has eye like markings just above its hind legs. And they appear to come in useful when the frog is attacked by birds, or the fearsome giant water bug, an insect voracious enough it can eat adult amphibians.
When approached the frogs puff up their body and raise their hind quarters to flaunt their large, false eyes. these false eyes are only part of the frog defence strategy. At the centre of each false eye is a black disc, which contains a gland that produces a toxin.
The chemical is so potent that a single gland can produce enough to kill 150 mice, and owls have been known to regurgitate whole frogs, such is the toxin power. So if the glare of the frog false eyes doesn put off a predator, their nasty taste might. idreddit.com