Saturday, February 6, 2016

Molting: Fresh skin every time.

All insects have segmented bodies made up of many small sections. Insects have three major body divisions, the head, thorax and abdomen. Mouthparts, eyes and antennae are found on the head, while legs and wings grow from the thorax. In some insects these body divisions are easy to see. In others they are not so separate. The antennae, which are often long and carry sense organs for touch and smell. The head also has the usually large compound eyes and some ocelli or simple eyes. The head carries several pairs of mouthparts, which are very important in distinguishing the insect order. Some are adapted for biting, with two mandibles, and some are modified to form a tube for sucking the liquid food. The thorax has legs and wings. The legs have spines and claws. The thorax carries a pair of wings. The wings are often colored and may have hairs or scales.

The outer covering of the insect is strengthened on all or some parts of the body by a hard cuticle, which protects the body, gives it a shape and as an external skeleton or exoskeleton provides a fixture for the soft body parts. This strengthened skin or cuticle consists of chitin and sclerotin. These two substances together form a very hard and resistant, but very light structure which in the course of evolution has served a variety of functions. Finally the cuticle is covered by a waxy layer, which acts as water repellant. 

This very resistant and powerful form of skin has, however, one great disadvantage. Once formed it can not be altered, that is, it can no longer grow. As the rest of the insect’s body grows, a new skin begins to form under the old one. When the insect molts, the old skin splits and the insect crawls out. The soft, new exoskeleton expands at first just like elastic, but once it has dried and hardened, it will not grow any longer. Some newly molted insects eat their old skins, other just leave them behind.

Yuwaraj Gurjar.

Giraffe Weevil.

This is an unusual beetle found in Yeoor hills (Sanjay Gandhi National Park, India) called “Giraffe Weevil”. It is called as giraffe as its abnormal long neck. It is very tiny insect just less than one centimeter, but very colorful and active. Its flight was also very funny and wobbling.

These are types of beetles known as weevils or snout beetles or elephant beetles due to their long mouth parts. These weevils are minute to large species as much as three inches. One of the commonest weevils we can easily find in our wheat grains. Many of this species are wingless but many others fly well. Males and females are usually similar in appearance. In some species male can be easily distinguished by the form of the snout, forelegs or antennae. The legs are moderately long for walking.

Normally these weevils lay eggs on the plants or inside the plants. But this particular species prepare cases of green leaf. First the leaf is cut across near the base, the cut reaching to the midrib or crossing the midrib from one margin only. Then it is folded vertically and the tips rolled in; an egg is then laid and the rolling process continues till the leaf, up to the cut. This forms a compact cylindrical roll with the egg deposited in the centre. No silk or gum is used and the insect works with legs and jaws in folding and packing the leaf. The roll is left hanging to the remainder of the leaf, the egg hatches and the grub feed on the leaf inside the roll. The roll subsequently dries and falls off with the pupa inside. August / September are the perfect month to observe these rolls and the adult insects in our forests.

As a defense mechanism, weevils have the habit of “shamming dead” when disturbed, the legs and antennae get folded close to the body and the insect drops to the ground. It is very difficult to find the insect in the thick vegetation.

Yuwaraj Gurjar.