When the sun sets, a moth comes out to feed. With its long proboscis (the tube-like mouthparts observed in some insect species) and swift flight, it looks like a phantom hovering amongst the flowers. Maybe you have observed them at night within the parks of Hong Kong?
This insect is the convolvulus hawk-moth - 𝘈𝘨𝘳𝘪𝘶𝘴 𝘤𝘰𝘯𝘷𝘰𝘭𝘷𝘶𝘭𝘪 (Linnaeus 1758). When feeding, its 10-cm long proboscis could be a problem for predator avoidance, as the moth probes flowers for nectar while remaining in stabilized flight in midair . Even though feeding midair may seem to be a vulnerable position, this is actually a useful adaptation, as many other butterflies and moths need to land on the flowers to feed. This, however, makes them an easy meal for ambushed predators like mantis and spiders. By hovering in midair, however, hawk-moths remain out of reach from the dangers hidden on the flowers.
But danger can still arise from the air. Surprisingly, these moths have developed hearing as a defense mechanism against predation! Moths are the favourite menu item of bats which locate them through echolocation. The moths, however, have developed an ear-like organ on their mouth parts enabling them to hear the bats’ ultrasound and react to them accordingly. Based on hearing they can judge the proximity of the bats as the intensity of the sound increases as it gets closer. The moths are swift flyers and they generate a humming sound while flying. These sounds would allow the bats to locate the moths. As the bat approaches, the moth would stop flying and hide, or fly slower, as an attempt to be more quiet.
When looking at insect mouthparts, we can learn a lot about their diet. The long proboscis of the moth is typical of nectar feeding used to probe towards the bottom part of the flower to the nectary, where the nectar originates. But what flowers do the convolutus hawk-moth specialise in feeding on? Several species including lilies, orchids and amaryllis, all sharing a common characteristic, a long flower tube! Therefore, when you see a funnel shaped flower, you can expect that it is pollinated by a hawk-moth. Interestingly, this species of moth is the main pollinator of Africa’s night blooming flowers, and this association drove a convergent evolution between night blooming flowers, leading distantly related flowers to evolve a similar appearance, all serving a similar purpose: attract the convolvulus hawk-moths. As pollination is the key to sexual reproduction in plants, flowers with traits appealing to the moth will have a higher chance of reproducing.
This co-evolution is not limited to the shape of flowers, but also to their colouration. As hawk moths are nocturnal and as light is minimal during nighttime, the colour of the flowers must reflect light in those conditions. Petals with white, pink or yellow colouration are most effective to attract the attention of moths. In addition, flowers will “guide” the moths for a successful probing and nectar collection through the display of a cross pattern marking , so the hawkmoth can accurately and quickly find the nectar. Then the moths stir the nectar with their proboscis and feel the viscosity of the nectar, with different types of sugar forming different types of nectar texture. If the texture is not right, they will not drink the nectar, but if it is the right type of viscosity, they will start their dinner. And that's how these picky eaters drive flower and nectar evolution.
Be sure to come and visit the convolvulus hawkmoth, and you see our specimen residing in the box with other astonishing moth species. And if you enjoy this post, please share it with friends and follow us for more amazing biodiversity stories weekly.
Text: Hugo Lee
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