Climes they are a changin'

The warm and vigorous south wind that played upon the island so voluptuously for a day or two earlier this month carried in from the Continent a host of Ireland's favourite "strange insect". In the most abundant invasion for many years, the progress of the day-flying hummingbird hawkmoths has been recorded with touchingly straightforward wonder.

In Boherbue, north Cork, Deirdre Hunt and her grandson Cathal stood among stately candelabra primulas to watch the amazing novelty that hovered at the flowers, pushing a long tongue into the bells. "It was about three inches and its wings moved very fast, creating an orange blur. The end of the body was black and white and Cathal said it was like a leopard's face. The tongue was held out horizontally. Its flight was jerky, rising and altering course abruptly as it went from flower to flower . . . "

Further north, in Glenealy, Co Wicklow, Michael O'Donnell walked out along the railway line and counted 84 of the insects, all whirring away at the clumps of red valerian. "It was amazing to see so many. They were almost as common as bees."

In Belfast, Brendan McSherry found one of "these wonderful creatures" in the hall of his house, "trying to suck nectar out of a colourful, wall-mounted display of old and foreign banknotes". And at his desk in the RSPB he answered calls from people who thought they might have seen hummingbirds.

In motion, Macroglossum stellatarum, does give a fair imitation of the world's tiniest and most agile bird. At rest, it becomes a large, stubby moth almost 6 cm long, with very dark and narrow front wings covering a pair of amber ones. The black-and-white "tail feathers" are lengthened scales of the abdomen, used for holding and changing position while hovering in front of a flower.

For rest, however, it needs darkness: it will fly in a lighted room but fall to the ground at once if the light is switched off. Otherwise, most of its life is spent in perpetual flight in daylight, no matter how hot or wet the weather, outdoing the hummingbird's energy at 50-70 wing-beats a second and pollinating perhaps 100 blooms in five minutes.

Compared to some of the flower-visiting hawkmoths of the tropics, with coiled tongues up to 25 cm long, the glossum of this species isn't really all that macro. But its eyes, according to some newly-published research, are quite remarkable and of "unsurpassed quality" for their type.

The compound eyes of insects, with their multiple facets, build an image with a mosaic of points of light. In one type, the "apposition" eye, each retinal rod receives light only through its own lens, to give potentially the sharpest picture (the first, somewhat fuzzy, photograph through a glowworm's eye was published more than a century ago).

In the other type, the "superposition" eye, the retinal rods gather in light from quite a number of adjacent lenses, which gives the brightest image but not such good definition. This is the structure, adopted by nocturnal insects, that gives such a jewel-bright glow to the eyes of moths fluttering at a lighted window.

The hummingbird hawkmoth seems to have married the best of both visions in a way that had been thought impossible. In the areas of its "superposition" eyes that it uses to fix on flower entrances while hovering and inserting its tongue, it has larger lenses and denser photo-cells to give the brightest, sharpest image with "outstanding spatial resolution".

The moth has been used extensively for experiments with flowers. They have shown, for example, that it will be attracted to the yellow flowers of toadflax even when these are sandwiched between glass to exclude the scent. It aims its proboscis directly towards the flower's deep-yellow honeyguide (just as the Belfast moth was, apparently, finding visual enticements in the colourful markings of banknotes).

Red valerian, honeysuckle, catmint, petunia, tobacco plants, true geranium - these are all deepthroated flowers that invite attention from Macroglossum, and from another hovering immigrant, the convolvulus hawkmoth, Agrius convolvuli, a few of which reach Ireland in June of most years.

The white trumpets of tobacco plants, Nicotiana, with their heady scent on warm, dark nights, have actually become dependent on the hawkmoths for pollination, and in Ireland attract Macroglossum by day and Agrius after dark. The convolvulus hawk-moth gets its name from choosing field bindweed on which to lay its eggs, and while one might think that white and strongly scented flowers would be the easiest to find in the dark, it is perversely able to find blue or violet flowers when it's so dark that they look almost black to us.

Some of the hawkmoths are decoratively marked with pink - the convolvulus hawk has pink rings on its thorax and the two resident elephant hawkmoths, large and small, are positively glowing with the colour. Despite their abundance in Ireland, flying from May to July, and their readiness to flutter at lights, the elephants as moths seem to attract little notice. As caterpillars, on the other hand, they reach an impressive size, ageing into brown, cheroot-sized beasts that puff up their eye-spots when disturbed.

Such an early arrival of the hummingbird hawkmoth (along with an influx of red admiral and clouded-yellow butterflies) promises a brood from the eggs they are laying now on lady's bedstraw, the sweet yellow-flowered froth of hedgebanks and sand-dunes. There may even be a late brood in the autumn. The moth "rarely if ever" overwinters in these islands, but, as with the migrant red admiral, global warming could soon produce exceptions. The climes, they are a-changing . . .