Not all our visitors arrive on foot. On Monday last, just as we were finishing up for the day, an unusual visitor arrived. Our volunteers, Mary and Harriet and Bernard the gardener, watched in amazement as it darted about and hovered, its wings flapping rapidly. Then it latched onto a Dianthus plant and fed on the pollen. We were puzzled, having never seen anything like it before. Was it a bird, a butterfly, a bee or a moth? In fact, it was a Hummingbird Hawk-moth, Macroglossum stellatarum (Linnaeus, 1758)
These summer visitors to Ireland are being spotted more frequently in recent years. According to Birdwatch Ireland, they are ” a scarce species of day-flying moth that does a remarkably good job of imitating hummingbirds.” So while they are moths, their feeding habits and requirements are similar to those of hummingbirds. As a result “they have evolved a similar body shape, flight method and feeding behaviour.”
It usually arrives in Ireland between June and September, coming from Southern Europe which is its natural habitat. There’s some evidence that it has bred here, as the larvae has been seen but generally it won’t survive a winter here.
The Hummingbird Hawk-moth has a wing-span of about 2″ and unlike most moths, it flies in daytime. It’s forewings are brown and rather dull looking but the hind wings are orange and this becomes visible when it hovers. It has a fan tail, which often adds to the hummingbird confusion when people first see the moth. Its wings move at the rate of 85 beats per second, faster than its namesake, the hummingbird, which has 50 wingbeats per second. This makes it an agile flier and studies of a related hawk-moth species, Manduca sexta have shown that they can fly as fast as 12 miles per hour. The rapidity of their wing-beats even emits a humming sound. (It also make them difficult to photograph). A feature that made this moth even more intriguing for us to look at was its habit of moving rapidly from side to side while hovering, called ‘swing-hovering’ or ‘side-slipping’. This is thought to have evolved to deal with ambush predators that lie in wait in flowers
We noticed also its long tongue, which isn’t a tongue at all but a “proboscis” which it uses to suck the nectar from the plant. It’s a tube or straw-like appendage which curls up when the moth isn’t feeding. But the length of it means the moth can feed on plants not available to bees or other insects, such as nectar-rich flowers with a long and narrow calyx.
The need to conserve energy to fuel its rapid wing-beats, has made the hummingbird hawk-moth a discerning feeder. The insect will return to the same flower beds each day at the same time, knowing which flowers to go to for the best harvest. Even on stems with multiple flowers, the moth has been known to keep track of each flower they visit in turn, so that they don’t waste energy by repeat sampling the same (empty) flower. Their need for the energy provided by the pollen is so great that they have even been known to continue feeding while mating.
We noticed another interesting feature, as shown in the photograph above, as the insect seemed to be looking at us even while it was feeding. Hummingbird hawk-moths have proportionately large eyes to help them find the best flowers to feed on. Unlike other moths, they have developed an unusual feature whereby the centre of the eye contains more photoreceptors than around the edges. These receptors are contained in tiny facets within a hemispherical pattern allowing it to see more detail directly in front of them. The dark spot or “pseudo-pupil”, which creates the illusion that the moth is following you with its eyes, appears when the group of facets absorb the light coming from your direction.
The Hummingbird-hawk-moth, Macroglossum stellatarum (Linnaeus, 1758), is one of many moths in the Sphinx moth family (Sphingidae), so-called because of the resemblance of their larvae to the famous Egyptian Sphinx.
Hummingbird hawk-moths sightings are becoming more and more frequent, particularly after any prolonged period of warm weather or warm southerly winds. Anecdotally, this is borne out by one of our volunteers, Sally, who recalls seeing them in the past in the Dordogne region in France but more recently in her garden in Crosshaven. Seeing a hummingbird hawk-moth is considered a good omen. On D-Day, 1944, during the Normandy Landings, a swarm of Hummingbird hawk-moths was seen flying across the English Channel. Good omen or not, we were delighted to meet this unusual visitor, up-close and personal. One of the many ways we continue to learn about nature in the Fota Frameyard.