Survival of the fittest

by K.S. Gopi Sundar

 

Caterpillars transforming into butterflies is nothing out of the ordinary. But it is not as simple as it seems.

 

Butterflies are perhaps the easiest to identify among all insects because of their vivid colours. Their life cycle is also famous. Caterpillars hatch from tiny eggs, and go on to become pupae from which, the winged butterfly emerges. But, as is always the case in the natural world, there is much more than meets the eye. Three species hatched out on a balcony in Delhi, each with their own strategy to avoid being eaten.

Survival instincts

The Plain Tiger butterfly chooses the Crown Flower plant ( Calotropis gigantea ) to lay its eggs on. The leaves of this plant store several poisonous chemicals which ensure that the plant is inedible to grazing animals. Plain Tiger caterpillars, however, can eat the leaves and store these chemicals in their bodies. The chemicals make them poisonous as well. Helpfully, the caterpillars are brightly marked signalling that they are poisonous.

While still young, caterpillars chew the leaves in a circle and stay inside – this helps form a moat within which they are protected by the leaf’s poisonous liquids. Most birds, therefore, avoid these young butterflies, and many are able to survive to the pupa stage.

The pupa is also magical in this species. It is green when the caterpillars pupate on a plant, and brownish when they pupate on something unnatural, like a pot. Camouflaging helps avoid predators during the pupa stage when the insect is unable to move for many days. The bright yellow-and-black Plain Tiger that emerges, has white spots on its body, all of which warn potential predators of the poison they carry.

The caterpillars of the Common Mormon butterfly thrive on curry leaves (Murraya koenigii ). Lacking poison, the strategy used by them to prevent being eaten is that of imitation – they look like bird droppings while they are young. As they grow older and approach pupation, the caterpillars resemble small snakes. They have markings that look like eyes, and an organ that looks like the bifurcated tongue of a snake. They behave like snakes quite readily when disturbed or touched, and also release a strong smell to discourage predators.

The tiny Red Pierrot butterfly has only recently increased in number in Delhi. This is because most people living in apartments keep potted Kalanchoe plants on window sills, roof tops, and balconies. This is the plant that the Red Pierrots lay their tiny eggs on. Like the Common Mormon, this species also lacks poison because of the host plants they feed on.

Red Pierrots are juicy and thick, and to avoid being eaten until pupation, the caterpillars have evolved a clever strategy: after hatching, they delicately eat into one layer of the leaf so that they can get into the thick leaves. The caterpillars stay inside, eating the fleshy middle layer until they are ready to pupate. They pupate on the underside of leaves, or in between the leaf litter on the soil. From the pale-yellow pupa with spots, the distinctly coloured red-white-and-black butterfly emerges.

Even a small balcony in the middle of a bustling city, if furnished with carefully-chosen plants, can serve as your own mini butterfly garden. Also, many butterflies use very common plants as their host, making it easy to set things up within minimal space. So, be ready for your garden to be devoured by voracious caterpillars, but with the promise of being rewarded with enchanting views of butterflies hatching out.

This article appeared in the Hindu in School on 8 July 2014.

Picture: It’s bedtime – A Plain Tiger caterpillar