The common knowledge about moths is that they are nocturnal and are naturally drawn to light sources. There is an exceptional genus of moths that are much different—the Macoglossum spp. are active during day time. They dart among flowers with the wings flapping in high speed that gives out a humming sound. They probe for nectar with their long proboscis. These behaviours make them more like a hummingbird than a moth!
There are about 100 member species in Macoglossum spp. of the Family Sphingidae—all of them have a strong thick body and are adept fliers with high frequency of wingbeats. In some species it can reach as high as 85 wingbeats per second, emitting a clear humming sound! They are good at hovering which allows them to sip the nectar in flight.
In addition, they have specialized proboscis which uncoils when sipping nectar. They are like environmental ambassadors that bring their own straws! The proboscis of some species can stretch some 30 millimeters, about the full length of their body! This is why they are literally named "moths with the long proboscis" in Chinese.
Hummingbird Hawk-moth Macroglossum stellatarum is a unique member of Macoglossum spp. featured by the bright orange hindwings. The little moth is an intriguing long-distance flyer! The species from Southern Europe and North Africa will migrate as far as to England and Northern Ireland for reproduction. Researchers have also found that Hummingbird Hawk-moth can learn to identify colours more quickly as compared to other pollinators. This skill allows them to identify which flowers contain the richest source of nectar, and is indeed essential for their survival when they migrate to a new place and in need of energy source to replenish as soon as possible!
In search of local Macoglossum spp.
In Hong Kong, there are only two records of Hummingbird Hawk-moth, both in the Peak around October and November. It is believed to be occasional cases. According to the literature, there are 18 species of Macoglossum spp. in Hong Kong, and only four are commonly seen. Although most are seldom seen, they are widely distributed among secondary woodlands, shrublands, fung shui woodlands and grasslands at altitude from 100 to 700 metres. Some even take shelter in mangroves or farmlands.
Local Macoglossum spp. are generally active from March through November. Their favourite food sources include Golden Dewdrops Duranta erecta, Lantana Lantana camara and Prickly Ash Zanthoxylum avicennae, which are all commonly cultivated in urban parks. So you may spot the moth if you pay some attention!
Darwin's unsolved mystery
Talking about Macoglossum spp., we shall also mention its close relative Morgan’s sphinx moth Xanthopan morganii –the famous Darwin's moth. The story began in 1862, when Charles Darwin, "Father of Theory of Evolution", received a specimen of Christmas Orchid Angraceum sesquipedale. The flower has a strange structure with a spur that extends backwards some 30 centimetres, with nectar at the far end of the spur. The question of how the flowers pollinate had poked Darwin ever since.
It was only much later in the 1990s that a scientist successfully recorded on Madagascar a Morgan’s sphinx moth sipping nectar from Christmas Orchid with a 30-centimetre proboscis, and left the flower covered with pollinium on its body. The mystery of how Christmas Orchid pollinates is finally solved a hundred years after the passing of Charles Darwin!