Threaten Sign    


Threaten Sign and Eyespots Pattern

Besides camouflage and mimicry, it seems that there are the third way to visually avoid the predators. It is to put on a Threaten Sign. 
By evolution process, birds draw the cat's face on moths' wings. 
Some insects, especially the moths and butterflies, they have the large eyespot patterns or face patterns on their wings. Those patterns resemble their predators' predators. Those patterns do not necessary make their predators believe that those insects are their own predators. The insects just bare a sign that its predator instinctively afraid of.
Birds are one of the major predators of insects. However, those birds have their own predators, such as a cat hiding behind the grasses, or a hawk suddenly appear from the sky. The birds, to survive, must recognize their predators within a fraction of a second, and with minimum cue. We believe that there are some signs or cues that are in-printed as the instinct of the birds. So that the birds can escape from their predators without too much of thinking. By evolution process, some insects exploit this birds' instinct and put on those Threaten Signs to avoid predation. 
Followings are some examples that we found. We did not find any literature to support this theory. We need more study on this area.

Predators' face on Moths' wings

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The above pictures are examples of moth wings with face pattern. There are two large eyes. The thick white lines may remind the birds of their predators' teeth. You may find more examples if you go through our Moths pages.

Predators' face on Butterflies' wings 

Watch the above butterflies wings patterns, with a little imagination, you may see the cat's face. There are the eyes and big mouths. One thing interesting is, most butterflies rest with wings closed. Those butterflies with cat's face on wings rest with wings opened. More information about butterflies please click on here.

Caterpillars mimic bird's predator's claw

Besides cat's mouth, cat's or hawk's claws are also deadly to birds. There are quite a number of different caterpillars will post the posture as shown in the above pictures when they are disturbed. Those postures do not necessary make their predator believe that the caterpillars are the hawk's claws. The caterpillars just post a sign that its predator instinctively afraid of.

Mimicking Predator's Face

Caterpillar: "Bird, dare you come closer?  I am a snake."
When looking at the beetle with the front view, we noticed why there are the round dome on each shoulder. Those domes mimic the eyes of a larger animal. The beetle spends long time on stem feeding plant skin. It will most likely encounter its predators, such as a bird, from above. The mimicking larger animal's face may scare away its predators.
The planthopper may not look like a jumping spider in the human point of view. Imagine if you were an ant or a jumping spider walking along the 10mm thick stem. When you met the planthopper, most likely you will see the planthopper face to face. At this angle, the planthopper looks like a jumping spider. 

Skull Pattern on Cockroach

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Even our human instinct is exploited by the insects. Let do a simple experiment. The above two cockroach pictures are the same except we had removed the dark pattern in the second picture. We find the cockroach in the second picture is far less ugly. Do you agree?
Most of us instinctively feel horrible when we see the skull pattern. We believe this is the instinct of most vertebrates. This pattern helps cockroaches to avoid vertebrate predators. 
This may also explain why some humans react to the cockroach much more than they should be.


Why we think Butterflies are beautiful but Cockroaches are ugly?

They need to be beautiful

Most butterflies are active in daytime. They have good eyesight. Visual attraction is the major way to attract their opposite sex. The more outstanding they look, the higher chance they win the appreciative of their sex partner and the better chance they will have more offspring.  For the butterflies lift style, evolution favor their beauty.

Moths are very close related with butterflies and have the similar body structure. They have large wings and scales. However most moths are active at night. Visual attraction is not so important to them. So most moths are not look beautiful and dull in colour. Interestingly, there are some moths active at daytime they are very colourful and sometimes considered they are butterflies.

Actually, not all butterflies are beautiful. Some butterflies species active after sunset, like the Evening Brown Butterflies, are not so beautiful. Their wings patterns look rather like a moth. Like moths, active at night, and they attract their opposite sex not by visual attraction but by some other means such as fragrance.

They can be so beautiful

Butterflies can be beautiful because they have large wings surface so that beautiful pattern can be shown on those area. Butterflies have scales on wings as moths do.  Those scales are believed to evolutes against the spider web. And those scales serve another purpose. Those scales can act as the small pixel so that high resolution pattern can be presented.

There is the disadvantage of being beautiful. Colourful means outstanding from background and will be easily seen by the predator. However, butterflies co-evolution with the plants. Most plants evolutes special taste or toxic to avoid leaf eaters. The butterflies evolutes so that they can accept those bad taste and toxic and they become bad taste and toxic themselves by storing those substance inside their bodies. Their beautiful pattern become a warning signal to their predator. 

Human instant

The most important reason for 'butterflies are so beautiful' is: it is the human instant. Butterflies are active only when there are sunshine and good weather.  Where there are butterflies, there always flowers and plants. This implies that there are foods, water, flash air etc., that we human need. Unlike some other insects, such as cockroaches, butterflies do not have big eyes pattern on the thorax, they do not have hairy leg and they do not hide in the dark. When we see butterflies, it always imply there are something good. We, as the mammal, evolutes with the butterflies for million year and it become our instant. So we always think butterflies are beautiful. This is the same reason why we think white cloud is beautiful and dark cloud is not beautiful.

Big eyes pattern on the thorax,  hairy leg, hide in the dark........ yes, cockroaches are ugly! 


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Last updated: February 25, 2007.