The image of a confused moth bumbling around a light bulb gives a false impression of the flying ability of these underappreciated insects. In fact moths are magnificent in flight, capable of aerobatic feats well beyond the ability of most butterflies.
Frozen flying
The Winter Moth (Operophtera brumata) is a very common species in Britain but one of only a few that have their adult flight period in the middle of winter. It is the male Winter Moth that you see in your car headlights, fluttering weakly in country lanes at this time of year. They must be males, as the female moths are flightless, possessing only tiny vestigial stubs of wings on their backs.
Most moths and butterflies need to maintain a high internal body temperature, similar to our own, in order to fly and have to spend time basking in the sun or shivering their muscles to warm up. If it is very cold then flight is either impossible or very energy demanding. However, the Winter Moth and its relatives are able to fly on freezing nights with body temperatures at or below 0°C and while using up very little energy. It seems that the large size of the Winter Moth’s wings relative to its body mass is the secret to this amazing ability, enabling the moth to fly with slow wing beats and low energy consumption in cold conditions.
Marvellous Manoeuvrability
The Humming-bird Hawk-moth (Macroglossum stellatarum), on the other hand, can beat its wings at an astonishing 80 times a second! Not only does this produce the audible hum referred to in the species’ name, but it enables the moth to perform incredible aerial manoeuvres.
Most familiar is the precision hovering flight used by the moth while probing flowers for nectar with its long proboscis. However, for me, the most impressive thing about watching a Humming-bird Hawk-moth at work is the combined effect of these brief, flawless hovers interspersed with rapid, darting flights, sometimes too fast for the human eye to follow, as the insect works its way from flower to flower.
What’s more, it’s not just high-precision flying at close quarters in which the Humming-bird Hawk-moth excels. It is also a long-distance migrant, regularly crossing the sea to arrive in Britain from warmer parts of Europe.
Intercontinental insects
Migration between continents and over large expanses of sea are perhaps the most impressive feats of flying undertaken by animals. And here, once again, moths can rival anything that butterflies can do.
R
ecent advances in understanding, gained through the use of vertical-looking radar, show that the Silver Y moth (Autographa gamma), for example, migrates northwards to reach the UK in the spring and returns south in the autumn. The numbers of Silver Ys involved in these movements can be enormous – in good years an estimated 220 million migrate into the UK in spring and three times as many depart in the autumn.
This is no unruly mob being blown hither and thither by the winds. Silver Ys use sophisticated senses and complex behaviours to ensure that their journeys are efficient and effective. As has been shown for the Painted Lady butterfly, migrating Silver Y moths choose the altitude (which can be over 1km above ground level) that provides the best wind direction and speed for their journey. In addition, if the wind direction is not quite right, the moths are able to orientate their bodies during flight to compensate and so maintain their preferred heading. Both these abilities imply that Silver Y moths must have an internal compass, although this has yet to be proved. If Silver Ys and other nocturnal migrant moths do have such a compass, it cannot work in the same way as those possessed by Painted Ladies or Monarch butterflies as they rely on the sun to orientate. Silver Ys and other nocturnal migrants may navigate by the earth’s magnetic field instead.
Richard Fox
Surveys Manager
Follow me on Twitter: @RichardFoxBC