The Caterpillar Curriculum

Peacock butterfly © P.Catton

A Case Study in Managing Change with Style

I wonder how many children have foregone the school curriculum during lockdown in favour of lessons in nature exploration and specifically, caterpillar husbandry.

From talking to others, I know we are not the only household where any suitable container is intercepted before it gets to the recycling bin and turned into a comfortable abode for butterflies and moths during their often-overlooked larval phase.

Walks in the park are now spent inspecting the underside of foliage for lurking caterpillars or looking for the tell-tale signs of rolled up leaves held together with silk to form a protective bivouac. As gardeners will no doubt attest, once you start looking, the signs of decimated leaves are everywhere. Yet caterpillars themselves are far harder to find. I suspect a part of this is because I’m not the only one looking for them, and the competition is far better at it than me.

The downside of being a hungry caterpillar is that you yourself are an energy rich snack. Although a caterpillar may ultimately consume 27,000 times its own body weight, it still takes a lot of them to feed a growing Blue Tit chick. In fact, nest monitoring has shown that a single chick may consume up to 100 caterpillars a day. This could equate to as many as 20,000 caterpillars to fledge a single brood!

Of course, caterpillars don’t take this onslaught lying down (figuratively speaking). Defences include good old fashioned camouflage, being unpalatably hairy, aposematism (where they use bright colours to alert predators to their toxicity),
Batesian mimicry (where they pretend to look like something more dangerous than they are) and thanatosis (where they play dead and tumble to the ground and safety as soon as they are disturbed).

As caterpillars grow, they regularly need to shed their skin to enable them to expand. Each stage between moults is known as an instar and the caterpillar’s appearance may change dramatically as these instar phases progress. At the final stage,
the caterpillar will unzip its skin for the last time revealing the chrysalis shell underneath. There are a variety of strategies for staying safe while in this state of frozen animation, from being well hidden, to creating protective silk cocoons, or even hiring some minders to take care of you. For example, the Common Blue butterfly chrysalis produces honeydew which is attractive to ants who harvest these pupae and take them underground to keep them safe in return for a sugary energy drink.

The really clever stuff is happening on the inside though. Throughout the caterpillar’s body it has smuggled blueprints and building materials in readiness for its ultimate magic trick. Imaginal discs are groups of undifferentiated cells, there is one disc for each body part that the moth or butterfly will need – wings, legs, thorax, abdomen.

Along with the caterpillar’s nervous system, these discs are all that remain after it literally dissolves itself inside the chrysalis. The soup provides the energy and medium to fuel these imaginal cells to develop into its adult form. Most amazingly, it is believed that the experiences and memories of the caterpillar are retained by the adult moth or butterfly, which is now able to disperse far and wide to breed and find suitable habitat for the next generation of leaf munchers.

So, if you are looking through your garden, out on reserve, or in a local park, don’t just admire the butterflies when you see them zipping past, but get to know them in their ugly duckling phase. Because the truth about managing change, is that
the beautiful end result is best appreciated when you understand the trials and tribulations it took to get there.

Not sure where to start?

Check out Common Nettle, it is a larval food plant for Small Tortoiseshell, Red Admiral, Peacock and Painted Lady butterflies.