A Closer Look at Butterfly Larvae

From 1st instar to 5th instar
Newly hatched caterpillar is called 1st instar caterpillar. The shell of the caterpillar cannot be stretched, so as the caterpillar continues to grow, its skin will peel off. Every peeling represents an increase of one instar. Caterpillars typically go through four to six peelings, and will pupae after the final instar (i.e., fifth instar).

1st instar

2nd instar

3rd instar

4th instar

5th instar

Interesting body structure
Though the caterpillar body structure appears simple, if you take a detailed look, you will find a lot of magic in its body.

• Head
  There are three eyes on each side of the caterpillar’s head, but they can only sense and distinguish light and dark, rather than viewing images. There is also a mouth, with which the caterpillar can chew leaves and test food. A silk-spinning organ can also be found on the head; with it, a caterpillar can create silk to hold its body in place, and make leaf shelters.
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• Thorax
  The thorax of a caterpillar can be divided into three sections, each with a pair of thoracic legs. A claw can be found at the end of each thoracic leg; this it will be developed into the adult’s foot, which is for walking later. In some butterfly species, the caterpillar chest is particularly thick, with a pair of spots like animal eyes: viewed from some distance, these make the caterpillar resemble a snake, deterring predators.
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• Abdomen
  The abdomen of a caterpillar can be divided into ten sections, with five pairs of abdominal feet. There are no sections on the abdominal feet, which are temporary features that disappear as the caterpillar transforms to the adult stage. Each abdominal foot is cup-shaped, which can help caterpillar to walk and attach to surfaces. The digestive, absorption and excretive organs are in the abdomen.
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Caterpillar loves eating
Butterfly caterpillars eat like a machine, the only thing they do every day is to "eat". After hatching, the first thing they do is eating their own egg shells. Eggshell is rich in nutrition, eating it can reduce wastage and can also prevent predators from discovering the caterpillars.

Most butterfly caterpillars are vegetarians, but they are very picky about what to eat; many of them only consume a few specific species or even one species, or even a single type of plant. If female butterflies lay eggs on unsuitable plants, after hatching, the caterpillars would rather starve to death, a choosy eater indeed! In addition to leaves, some caterpillars will eat the flower bud. For instance, Toothed Sunbeam (Curetis dentata) caterpillar likes to eat flower bud in red colour, so even its body appears to be pink. Some butterfly caterpillars are carnivorous, they will prey on insects that are smaller in size than themselves.

Common Jester (Symbrenthia lilaea) eating Ramie

A Swallowtail caterpillar eating Mandarin

Home of caterpillar
Butterfly caterpillars live in their food plants until they pupae. In order to escape from predators, some clever caterpillars will spin, tow the leaves together, make a leaf shelter, and live and pupae inside the shelter.

Leaf shelter of Pale Awlet (Burara gomata) caterpillar

Caterpillar self-defence skills
Many butterfly caterpillars are green, enabling them to hide in the foliage; some even “dress up” as part of a leaf vein to hide from predators. Caterpillars often have stripes, and the appearance of a single species will vary during different stages of growth.

Butterfly caterpillars are food for many birds and insects, so to increase their survival chances, small caterpillars will develop into a unique shape. Caterpillars from the Papilionidae family (Swallowtails & Birdwings) are excellent mimics, disguised as bird droppings when small. The more mature caterpillars imitate snakes: on the head of each is a pair of fake snake eyespots, and a forked fleshy organ called an osmeterium, which looks like a snake's tongue, appears when they are disturbed. The forked osmeterium can also release a foul odour to deter predator. Caterpillars from the Danaidae family (Danaids) are toxic, they are usually brightly coloured, warning predators to stay away. Some non-toxic caterpillars mimic Danaidae caterpillars, so that predators will believe they are toxic.

The head of a Blue caterpillar is hidden under the chest, so that predators find it difficult to distinguish between head and tail, reducing the chances of the head being attacked. Caterpillars of Browns have two antennae-like tails, which can also confuse predators trying to distinguish the head and tail. Some caterpillars of Nymphs have uneven surfaces, some have thorns on the head, and some have thorns all over the body. The weird shapes of these caterpillars make them hard for predators to swallow.

Osmeterium of Spangle (Papilio protenor) caterpillar

Small Swallowtail caterpillars look like bird droppings

Caterpillar of Plain Tiger (Danaus chrysippus) is colourful, to warn predators that it is poisonous

Observe caterpillars
Similar to eggs, tiny caterpillars are always being overlooked because they are not visible. In addition, it is especially difficult to discover caterpillars of 1st and 2nd instar because they are extremely tiny. To observe caterpillars, we need to distinguish different plant species, because different caterpillar species can be found on different food plants. We can pay attention to the tenderest part of the leaf, which is the tip, and see if there are holes and bite marks. If so, there is a big chance to discover caterpillars. We may check out the underside of the leaves, as some caterpillars love to hide away from direct sunlight and a cool place. In addition, if leaf shelters are found on the leaves, you can carefully check if there are caterpillars inside.

Caterpillar of Common Mapwing (Cyrestis thyodamas)