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.
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.
How many strategies do butterflies use to avoid predators?
On studying the butterflies, we observed the following strategies that butterflies use to avoid predators. Compared with other insects, butterflies are colourful and with different pattern. Some of their escaping strategies are based on the variety of colour pattern.
Eye spot pattern
Eye spot patterns are common in butterflies. Many species have this pattern on top side, underneath or both side of their front and hind wings. Those spot help the butterflies to survive in two ways. Some butterflies have two big eye spots on their hind wings. When they are at rest, they cover the eye spots by the front wings. When a predator come close, the butterfly will suddenly show the eye spots, to scare them away. Some other butterflies with only small eyespots. Usually those spots are on the edge of their wings, the less critical part of their body. Those spot are used to puzzle the predator to use it as target. If being attached, the butterfly just loss a small bit of wing edge and fly away. Sometimes we find find a Evening brown butterfly with a small triangular price of wing is missing, just like being biten off by a bird.
Some Butterflies have tails on their hind wings, such as the Swallowtail butterflies and the Coppers. Some of them, their tail and their eyespot pattern, may be confused as antenna and eyes by some predators, and predict their moving direction wrongly so that they can fly away.
Being poisonous and with warning colour
Some butterflies, like the Wanderer, is poisonous or distasteful. It is an advantage if they can be easily distinguished by their predators. The bright colors serve to warn birds or other predators that this butterfly is bad-tasting.
The Common Crow and the Dwarf Crow look similar. In some case two different but both are distasteful butterflies evolved to mimic each other. This enhance the warning colour effect. In other cases, other butterflies, although perfectly edible, may have colours that mimic the bad-tasting species and therefore gain protection for themselves. Mimicry is a interesting evidence of evolution.
The Evening Brown is hardly seen when it rests among the dry leaves. Certain color patterns may help the butterfly blend into its background and be protected from birds or other would-be predators by "background resemblance."
Some butterflies are flying very fast. Their flying pattern is different with those butterflies with warning colour protection. We can see the Wanderer gliding in the air but will never see the Blue Triangle flying in straight line. The Blue Triangle flying very fast and in a zig-zag path. Its wings will not stop flicking even it stop and visiting a flower. We can catch the Wanderers much easier than the Blue Triangle.
Scales to escape from spider wed
We seldom see the butterflies caught by the spider web. The scales on the butterfly wings are the major reason. The butterfly scales are important weapons evolved to defend them from the spider web.
Why most butterfly caterpillars rely on single or very few type of host plants for food?
Like some other insects, butterfly caterpillars eat only very few type of host plants. The Wanderer caterpillars only feeds on the milkweed plants and the Birdwing caterpillars only feeds on the Birdwing Vine. This single host plant phenomenon is very common in butterflies and it is not an advantage to the butterflies. We observed the following situations that contributed to this phenomenon. The following discussions can also explain why parasites are usually specialize on a single host type.
Plants Defend, Insects adapt
We, mammals have our immunity system to defend us from parasites. Plants evolved their way against being eaten by insects and other herbivores. They change their physical structures and chemical contents to avoid being eaten. Some plants may have hairs or wax on their leaves. Some plants may make themselves have a bad taste or even toxic. However, the herbivores, like caterpillars, must rely on the plants for food and they have to evolve to adapt to the plants changes. Then some insect herbivores become specialized on few type of plants. This also explains why introduced weeds can be so successful for they do not have natural herbivores in the new environment.
Adults choose, Caterpillar eat
Grasshoppers are herbivores but most of them feed on many kinds of plants. The major different between grasshoppers and caterpillars are that grasshoppers can choose their own food. If they do not like the plants they are eating, they can move to another type of plants. The caterpillars do not have the right to choose. They can only eat or die. The selection is totally up to the adult butterfly. For example, the Birdwing butterflies in Queensland, the female will mistakenly lay egg on an introduced weed, Dutchman's Pipe, which the butterflies may think it is Birdwing Vine. The Dutchman's Pipe is poisonous to the Birdwing caterpillars and this is one of the reason that drove the Birdwing to become an endangered species. Another butterfly, the Blue Triangle, are not so selective, they lay eggs on many different kinds of plants. Some of the caterpillars cannot successfully develop. However, most of them can and this not-so-selective behavior help the Blue Triangle be one of the popular butterflies in Brisbane.
Competition between species
Another reason that makes the butterflies specialize on few host plants is the competition between species. If two herbivores rely on the same host plant. Eventually one species will drive the other out of the competition. The losing species will either switch to another host plant or become extinct. Both winning and losing species will become more relied on fewer host plants.
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