Reader’s caterpillar mystery solved

Elephant Hawk moth
Elephant Hawk moth

I received a lovely letter, along with some photographs, from a lady who obviously reads this column. The pictures were of a large caterpillar but, as she said, she had never seen anything like it before and was very curious to know what it may be.

Yes, large – around 3in long, khaki green to brown in colour, with a delicate network of black lines resembling broken glass all over, and with four large black and white markings resembling eyes. When startled, the caterpillar draws it ‘head’ in to its body, so resembling a snake with a large head and four huge eyes! On its final segment (back end) the caterpillar has a backward-curving spiny ‘horn’, or ‘trunk’ – so giving the larva of our Elephant Hawk Moth its name. These defences are known to deter predators, and certainly make it one of our most impressive of moth larva.

The Elephant Hawk Moth is one of the largest moths found in the UK. Part of the Sphingidae family, it includes almost 1,500 species of which most are found in tropical regions. They are all quite large moths, and certainly amongst the most impressive in our country. The common name of ‘hawk moths’ refers to their rapid and sustained flying ability. Their other common name of ‘sphinx moth’ comes from the larva’s method of ‘resting’, holding its legs off the surface of the branch and tucking its head underneath – so resembling an Egyptian Sphinx. Like the Elephant Hawk Moth, many larvae, particularly of the even larger tropical species, are thought to mimic snakes.

I have to admit, I recognised the subject of the photograph immediately. I first ‘found’ one many years ago on a holiday in Scotland. He was crossing the road – and yes, he had me mesmerised for I had never seen such an impressive caterpillar before! He came home with me to pupate, as I knew he was heading for a place in which to undergo his metamorphosis through the winter. However, I had a bit of a shock in the spring, for instead of the beautiful moth I was expecting to emerge, the top of the pupae was ‘cut off’, as if by a can opener, and there, in my cage was a dramatic black and white wasp. The adult of which had obviously laid eggs in my wonderful caterpillar, for its own larva to eat the protein soup of the pupae. Parasitic wasps are actually just part of the natural ecosystem and we actually use a number of species of these in horticulture to naturally control pests, such as glasshouse whitefly. But it certainly upset me at the time (I was only about eight or nine)!

So Mrs M’s caterpillar has had the summer feasting, most probably on willowherb, although they do also eat fuchsias, and was heading off to pupate. They will spend the winter in this stage, often underground or in crevices among rocks or logs. The adults will emerge in the spring to mate and lay eggs on the willowherb, as this too disappears underground for the winter – yet can reach well over a metre by the end of its growing season.

Happy gardening!

n Manea School of Gardening

is an RHS approved centre.