The very hungry caterpillar is quite fussy about its food
ANOTHER LIFE:AT REST IT LOOKS, for those who remember such things, rather like a small, dark cheroot, of the kind once – perhaps still – clamped between the shiny teeth of Mexican bandits. Close up, however, its skin has the sheen of a soft velour, patterned with moth colours like a 1920s sofa. And when alarmed, in a quite absurd simile of its own, it pulls in its snout and puffs up its eye spots to look as much like a menacing snake as a caterpillar can.
This autumn seems to be good for spotting the larva of Deilephila elpenor, the elephant hawkmoth, judging by the number of reader reports, some full of the awe of a first encounter. This is, indeed, one of Ireland’s largest native caterpillars, growing up to 7cm, and much more often seen than the hawkmoth that begets it. That’s a pity, as the moth is a beautiful arrowhead of bright pink and gold wings, seeking nectar in flowers by night and able to tell their colour even by starlight.
Not that the bright, long-tubed honeysuckle that fits the hawkmoth’s tongue especially well would take much finding. But the really important plants of its life are chosen to feed its caterpillars, not itself, and neither rosebay willowherb nor fuchsia exactly shines in the dark. Soon after a ghostly midnight copulation, which can last up to two hours, the female starts laying her glossy green eggs, continuing for several nights until she has deposited about 100, one by one.
The bond that most butterflies and moths have with particular plants to feed their larval stage is part of the relationship between plants and insects that powered much of the diversity of the natural world. Buy a field guide to caterpillars (Collins does the standard one, by Carter and Hargreaves) and you find colour plates bright with the caterpillars that feed on particular groups of trees and plants.
The cabbage whites seem obvious, but the food-plant index runs long, from alder to zea (maize), each with its own lepidopteral consumers.
Some species make a wide choice among quite separate groups of plants, but the bonds can be so exclusive that the very survival of a butterfly species depends on the existence of the plant and conservation of its habitat. In Ireland, for example, only the devil’s bit scabious of wet grassland feeds the black caterpillars of the endangered marsh fritillary butterfly.
Such close affinities have encouraged the idea of co-evolution between these insects and their food plants, with some even proposing that butterflies and moths reached the peak of their development at the same time as the flowering plants. But study still goes on as to why, exactly, such partnerships were formed and still endure. Taken to America, Europe’s cabbage whites insist on laying eggs on sulphurous European brassicas instead of switching to native species.
What is it about rosebay willowherb, for example, that so appeals to the elephant hawkmoth? This plant can sweep a lovely pink haze across a hillside of clear-felled forestry. I have admired it in the summer of the Greenland wilderness. It is the postinferno “fireweed” of Canada, and, having flourished on the bomb sites of London, it is now that city’s county flower.
Is it the plant’s chemistry, structure, nutritional quality or parasite-free space that makes it fit so well, and that makes fuchsia, an alien shrub in these islands, an acceptable alternative? (For some British gardeners, indeed, the caterpillars’ appetite for fuchsia makes it a pest.) While blossoms themselves may play little part in the diet of caterpillars, it is the emergence of flowering plants (angiosperms) and their interaction with pollinating insects that has been credited with the great surge in the planet’s insect biodiversity. But in 1995 came the apparent discovery, in a petrified forest in Arizona, of bees’ nests and wasp cocoons fossilised into the trees and 100 million years older than fossil evidence for the earliest flowers, from some 140 million years ago.
Enough sober and prestigious American scientists were sufficiently impressed to put legs, so to speak, under the possibility that bees could have evolved before there was nectar in the world, or colourful petals to lead the insects in. Before the flowering angiosperms, the planet’s vegetation was the lush greenery of the gymnosperms, mostly conifers and ferns. Harvard’s eminent Stephen Jay Gould, always ready for a scientific challenge, was quite open to the possiblity that early bees were already pollinating gymnosperms. The angiosperms, perhaps, developed new ways of attracting their visits.
By 2006, a rival camp of palaentologists had inspected the Arizona fossil cells and declared them more likely to have been left by some Triassic beetle-like creature.
In any case, Dr Stephen Hasiotis, their discoverer, continues to lecture at the University of Kansas. One of his geology students describes him as wearing “a fanny pack, skin-tight jeans, a Hawaiian shirt and boots everyday” and being “fairly funny”. None of that, of course, makes him wrong.
Eye on nature
On a boat trip around the southern tip of Clear Island, about a mile offshore, we saw a huge, blue-black turtle on the surface, about equal in size to a cow. It began to swim after us with its head out of the water on a long neck with its mouth open.
Robert Henaghan, Galway
It was a leatherback turtle, which can be two metres long and weigh up to half a tonne. They make an annual migration along the south coast and into the Irish Sea, from tropical breeding sites, in pursuit of the barrel jellyfish (Rhizostoma pulmo), a favourite food.
I thought a recent visitor to my home was a moth. It was light brown, about 3cm across and looked like a stick.
Róisín de Leastar, Rosscarbery, Co Cork
From your photograph, it was the convolvulus plume moth, Emmelina monodactyla.
Recently I have been observing a black rabbit in my garden eating grass with a brown rabbit. A friend in the Kilbride area of Co Wicklow has seen black rabbits in that area.
Niamh Neumann, Newcastle, Co Wicklow
A very small percentage of the rabbit population is black. They tend to get picked off by predators more often than the grey/brown ones.
Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email email@example.com. Please include a postal address