The variation of insect's world

Tags: beetle | butterfly | cricket | insect | walking stick

Metamorphosis is an important process in insect's life cycle, because morphology and physiology of insect are quiet different in different stages. Butterflies and stag beetles are complete metamorphosis insects with pupa stage; as for crickets and walking sticks are incomplete metamorphosis insects whose larvas are similar to adults. We can learn the secrets of insects by understanding more about them. 

Insects form the most species-rich group of living organisms in the world. They are mainly divided into two parts, complete metamorphosis insects and incomplete metamorphosis ones. Insects that undergo complete metamorphosis like butterflies and stag beetles have pupa stages while the larva (called nymphs) of crickets and walking sticks resemble their adults in the process of incomplete metamorphosis. 

The abundance of species and the variety of different stages in the life cycle of insects have made them the most diverse group of living beings on earth. It is truly worth our devotion to further studying about them. 

【Walking stick】 Some walking sticks are all female and reproduce by parthenogenesis. So far there were no males recorded in many species of walking sticks. Thus female walking sticks of these species produce offspring from unfertilized eggs without the process of copulation. 

Walking sticks are exquisitely good at camouflage. Usually they disguise themselves as the twigs of trees. When the wind blows, they swing just like twigs do. They swing from side to side, and the harder the wind blows, the more they swing. Another special skill walking sticks develop to protect themselves from predators is giving up their appendages to save lives. 

If a walking stick is caught by its predator on the leg, it would give the leg away to its enemy. Nymphs then regenerate new legs little by little every time they molt. But adults have lost the ability to regenerate their appendages. Upon facing dangers, some species would even secrete thick odor of ginseng from glands on the anterior protergum to scare the predators away. 

【White butterfly】Pieris, the whites, is a widespread genus of butterflies. They are found everywhere in the world. In Taiwan, they are also the most commonly seen butterflies around the whole island. Many species have caterpillars which feed on leaves of the family Brassicaceae. Thus the crop-damaging species is often considered as pests by farmers. However, when the adults sip the nectar of flowers, they are perfect matchmakers for the plants. Without whites’ help, some plants can't even propagate. 

Whites produce a type of chemical called pheromone to attract their mates just like most of the insects do. They give off special smells, which travel to further distance through the air to attract the opposite sex. At close quarters, whites identify one another by sight instead of scent. The females and males of whites might look alike for humans. In the whites’ eyes which can see through UV light, the opposite sex is so different that they can easily distinguish one from the other at the first sight. 

【Plain Tiger】Plain tigers spread widely all over the world. Larvas are fearless of their predators at all because the caterpillars feed on poisonous plants and accumulate the poison inside their body through their whole lives.

The adults therefore fly slowly and leisurely near the ground. Besides, the caterpillars wear horrifying warning colors and have exaggerated spines to scare off the predators. Once the inexperienced predators attack the caterpillars, they would have diarrhea and feel very painful. 

Female and male plain tigers may look alike but are not impossible to be identified. When you squeeze the end of the abdomen of male plain tigers, the pheromone-producing brush-like organs would be pushed out. The coloration on their hindwings of male and female is quite different. Males have a number of secondary sexual characteristics on their wings. The biggest black spot, also at the lowest among the four on the hindwings is unique to a male plain tiger. In the ventral side of the hindwing of a male, there is a white plaque which is not seen on female. 

【Cricket】 Crickets, nicknamed “Chiu-chiu-er” in Chinese live in soil or underground tunnels. Their chirping and fighting habits had made them extremely popular in China from the old times. They are often kept as caged pets. And honored as the champion bugs in the world by the Chinese people. 

Male crickets chirp while females don't. There are ridges or "teeth" that act like a "comb and file" instrument on the forewings of the male. The chirp is generated by raising their left forewing and rubbing it against the upper hind edge of the right forewing, which has a thick scraper. 

Male crickets make two different kinds of sound, one is to threaten the same sex and the the other to attract the female crickets. When two rival males meet, they raise their wings and make displaying sound first. Then they wrestle and bite each other with strong jaws. They often got broken legs after the fighting. 

Crickets chirp. But how do they hear? Do crickets have ears? The answer is yes. To hear the call, a cricket has hearing organs located on its front legs. And the hind legs are very strong that make them great leapers. 

It is very easy to tell a female cricket from a male. Female crickets don't chirp. So their wings are without ridges and look smoother. And because females are responsible for laying eggs, they have a long needlelike egg-laying organ, the ovipositor, since they are in the larval stage. 

【Stag beetle】Stag beetles show phototaxis at nights. They are famous for their distinctive mandibles found on the males of most species. Male stag beetles use their jaws to defense themselves or to wrestle each other for favoured mating partners with the same species. Female stag beetles are more nervous and aggressive in nature. 

But they are normally harmless because their mandibles are smaller than the males. They often do fake death when they encounter potential enemies. Female stag beetles feed and lay eggs on tree bark or rotten wood. The larvae then feed on the rotten wood. Later after the adults crawl out of the wood, they turn to eat fruits and tree sap. 

The sizes of adult stag beetles differ according to their nutrition in larval stages. The better nutrients they were provided, the bigger they grow. Normally bigger male adults are fiercer but stable. When they bite, it is often a sign of warning. Smaller ones on the contrary are more nervous and easily irritated. They are more likely to bite people at random.

 

臺灣大學昆蟲標本館典藏數位化計畫

Digitalized Insect Museum-Bugs Recall http://www.imdap.entomol.ntu.edu.tw/

 

Walking sticks are so good at camouflage that we can hardly identify them in natural habitats when they are not moving. Adults of some species have wings while some don't. But they are not good fliers even with wings, they usually glide. 

 

 

 

 

Many walking sticks are careless when they lay eggs. They can be walking while laying eggs. Their eggs then might be scattered on the ground just like droppings. In captivity, there are sometimes eggs mixed with dung to be cleaned. But it is easy to pick the eggs out because they are always in regular size. 

 

 

 

Walking sticks are incomplete morphogenesis insects. Their nymphs resemble the adults in appearance only without wings. But for some species that the adults are wingless, hence it is harder to distinguish the immature from the mature ones, except that the nymphs are normally lighter in coloration. 

 

 

 

 

 Though the walking sticks are exceptionally good at camouflage, it is possible for them to be attacked by predators. Thus their strategy of giving away appendages for lives is very helpful. Almost all the insects can regenerate their lost legs during the process of molting. Walking sticks are no exception. But it seems that walking sticks tend to break their legs more often, and are better at regenerating than any other insects.

 

 

 

The caterpillars of white butterflies are nicknamed green worms. Many kinds of vegetable we eat are also their food. They are such eating machine that sometimes they eat up all the leaves of their food plants and leave only the veins. No wonder they are notorious pests for vegetable. The characteristic that they are not picky about food makes them good insects to be kept for observation.

 

 

 

The whites spread widely that we can see them easily no matter in mountainous area or near sea side. But they are so alert that as soon as you go near them, they fly off almost straight away . So it is not easy to observe the adults closely. 

 

 

 

 

 The eggs of all members of Lepidoptera including butterflies and moths have special shapes and patterns. The whites are no exception. Female whites seek suitable places to fix their eggs. The plants that provide food for the caterpillars after hatching are their choices. If you look at the underside of leaves of the family Brassicaceae, there are good chances that you would find eggs of the whites.

 

 

 

There are two kinds of pupae of butterflies, succinct pupae and suspended pupae. The pupae of whites is succinct pupae, which stick upwards, held in place by a silk thread around the dorsal side. When pupation takes place, the dorsal side of a pupa splits and the fully-formed imago emerges from the pouch. The butterfly then waits for the wings to dry out and harden.

 

 

 

The coloration of caterpillars of plain tigers is very bright and showy. But they are not afraid of their predators at all. The caterpillars feed on milkweed which is poisonous and keep the accumulated poison within. If the predators attack them, the alkaloid would intoxicate the predators and cause serious diarrhea. That is why they have no need to worry about their enemies.

 

 

 

 

 

The adults of plain tiger are brightly colored and easily noticed. But they don't have to worry about being attacked by their predators. The poison they accumulated from larval stages keeps working in their bodies. The adults feed on nectar only and no additional poison is ingested during this stage.

 

 

 

The eggs of all members of Lepidoptera including butterflies and moths have special shapes and patterns. The plain tigers are no exception. Plain tigers feed on milkweed only. The females thus lay eggs on milkweed. Just like other Lepidoterans, the newly hatched larvae eat part of their shells first before gnawing the leaves.

 

 

 

 

There are two kinds of pupae of butterflies, succinct pupae and suspended pupae. The chrysalises of plain tiger hang head-down with the end of abdomen stick to leaves. During pupation, the dorsal side of pupae crack open and adults emerge from the cleft on account of gravity. The newly emerged adults then hangs down with their heads up and wait for the wings to dry out and harden.

 

 

 

The male crickets chirp using their ridges and scrapers on the forewings. The pattern of their wings is thus quite complicated. The purposes of their chirping can be divided into attracting the opposite sex and warning to the same sex. The 2 sounds are obviously different.

 

 

 

 

Crickets lay their eggs in the soil hence the eggs are not easy to be found. With the protection of soil, the shells of eggs are comparatively thin. Without other protective structure on the shells, the changes within the eggs are visible. We can easily observe the well-developed nymphs that are ready to hatch from the outside.

 

 

 

The nymphs of cricket in larval stages resemble their adults except that they lack wings. It is easy for us to distinguish their sexes. Male nymphs have two cercuses in the end of abdomen. Female have an extra structure that will develop into ovipositors later between the cercuses.

 

 

 

 

Crickets are stridulating insects. Besides making sound, they have to hear the sound others make. The hearing organs of crickets are not on their heads but on the front legs. The small white membranous organs receive stimuli of sound. And crickets can detect sound through these special ears.

 

 

 

The male stag beetles use their strong mandible to fight and defense themselves. They fight mainly to get mate against their rivals. Females don't fight on the other hand; hence their mandibles are not as big as males’. But the smaller yet wider mandibles are more powerful tools for chewing wood. 

 

 

 

Eggs of stag beetles are usually hidden in rotten wood. Even the vulnerable newly hatched larvae would not need to worry about predators. The larvae twist with force in the eggshells and crawl out of the shell like shedding the membranous pouch. The newly hatched larvae look snowy transparent because they have not eaten anything yet.

 

 

 

The larvae undergo three instar stages. The third instars might be bigger than their adults. We can see the food they ingested from the transparent skin. Besides, each female third instar has a yellow pouch in its abdomen, which is a critical feature of females. This pouch will grow and become the ovary in the future.

 

 

 

 

Generally the female stag beetles lay their eggs in rotten wood. They bite the tree bark to form cavities to hide their eggs. The hatched larvae gnaw through the wood and spend their larval stages there. The eggs of stag beetles are white and round-shaped with a diameter of about 0.5cm. It takes about half a month for the laid eggs to hatch.