‘Speed Merchants’

Most people know which are the fastest-flying birds – Peregrine Falcon Falco peregrinus, 390km/h in a dive, 110km/h in level flight, The familiar Spur-winged Goose Plectropterus gambensis, clocks in at 143 km/h. Likewise mammals, where the Cheetah Acinonyx jubatus is undoubtedly the king of speed. But what about butterflies and moths? Slow, fluttering, gentle creatures, aren’t they?

Slowcoach butterflies

It’s true that some butterflies are definite sluggards. We have a particularly slow species in our area.

African Wood White Leptosia alcesta inalcesta is one of our slowest butterflies. They are often seen in the forests around Kloof and Durban flying low with leisurely wingbeats. They are reminiscent of the butterflies in the Disney movie Fantasia, and their Afrikaans common name Fladderpapiertjie (literally, ‘Little Butterfly Paper’) is oh so descriptive!

Black-haired Bush Brown Bicyclus safitza safitza is another slow flying forest understorey butterfly. They aren’t quite as slow as the African Wood White, and they are often found dancing slowly around in circles in groups of two to six. They make me think of Tolkien’s mind picture of ‘Hobbit children dancing the springle-ring’.

I couldn’t find any speed references for these species but the consensus on the Internet seems to be that most ‘normal’ butterflies have flight speeds of between 5km/h and 15km/h. Anyone familiar with these two slowcoaches would agree that they must be around the bottom of that scale, or even off it.

Our local rarity, Yellowish Amakosa Rocksitter Durbania amakosa flavida, relies on camouflage to avoid being seen. If disturbed it will raise its wings and flick them open to display orange-red patches like this male is doing. Females happily sit still, waiting for a male to find them. The males do fly, but very slowly with rapid wingbeats not moving them very far or fast. They only need to patrol a patch of rocks no more than a few tens of meters across, which doesn’t require an afterburner! If attacked they close wings and drop quickly onto the rocks, crawling downwards with closed wings.

Many small butterflies don’t move far and don’t need a turn of speed – their wing muscles are quite weak. But there are a few rapid ones… very rapid, as we will see.

The ‘speed merchants’

I remember my teenage days of riding high-speed motorcycles on British roads. Sometimes I got ‘nicked’ for speeding with the policeman smirking as he ticketed me with the sarcastic comment of ‘you’re a real speed merchant aren’t you sonny?’.

Like birds and mammals, butterflies and moths have their ‘speed merchants’. People have measured their speed, as I found by asking Mr Google. The flight speed of some of our local species is known.

Male White-barred Charaxes, Charaxes brutus natalensis, in typical pose perched high on a large plant alert to the presence of rivals. These butterflies can get airborne very quickly because they are already high up. All they need do is start flapping and they’re off!

One of our most attractive local butterflies, a male Blue-spotted Charaxes Charaxes cithaeron cithaeron.

This beauty is perching on the edge of the canopy on the hilltop near Rumdoodle, at the end of the Uve Trail in Krantzkloof Nature Reserve. This is one of the best places to observe high speed butterflies because the view site is level with the forest canopy. They dispute the airspace with other aeronauts like Swallowtails, Paradise Skippers, and Sapphires. Big Charaxes like these can outmanoeuvre even rapid birds like Swifts and Swallows. They fly with bursts of powerful wingbeats interspersed with short glides during which they can jink and dodge with aplomb. A male White-barred Charaxes has been clocked at 65km/h, according to a Florida State University article. These are large butterflies with wingspans in the 60-75mm range.

Here are two of the most rapid butterflies we have, perching on the canopy edge, again near Rumdoodle. To the left is the African Paradise Skipper Abantis paradisea, and to the right Bicolored Paradise Skipper Abantis bicolor. Wingspan is 36-41mm.

Close up of a male Bicolored Paradise Skipper. His short, streamlined wings, and deep thorax (chest) containing powerful flight muscles, are reminiscent of a fighter plane.

Skippers like these are the epitome of speed. They are among the fastest flying butterflies. At 60km/h they are in the same league as a Charaxes, but being smaller, their wings need to beat a lot more rapidly to move them around. They have reflexes twice as fast as a human’s (according to Dr Huertas of the British Museum of Natural History). Krantzkloof is one of the few places one can be fortunate enough to get close to the near-threatened Bicolored Paradise Skipper near its commoner but no less impressive relative.

Long-horned Swift, Borbo fatuellus fatuellus. A very fast skipper, looking very aircraft-like as he perches on an Agapanthus leaf in my Gillitts garden. These are just as fast as the slightly larger Paradise Skippers but are much commoner in our area. It might be said that they are more often seen, but they are SO fast and inconspicuous that they generally go unnoticed. Their aerial battles take place at low altitude; if you see two or more little ‘atoms’ racing around your garden, it’s probably these butterflies.

Southern Sapphire is one of our gaudiest small butterflies.

Southern Sapphires, the same wingspan as Paradise Skippers but with broader wings, are often seen flying at speed near hilltops and over the forest canopy. Their wings flash white and blue in the sun and when at rest on a tree with shiny foliage they are surprisingly well camouflaged. They often take on butterflies much larger than themselves, like Charaxes, and if two of them encounter one another, an aerial ‘dogfight’ ensues. They whizz around like little jet fighters and the scale speed is probably like that of an F15. It’s special to see them whirling into the sky flying upwards in tight circles until they disappear from sight.

Brilliant Gem Chloroselas pseudozeritis pseudozeritis is another of the Lycaenidae, but another subfamily, Aphnaeinae.

Photo: Mark Liptrot

The Brilliant Gem is a really tiny butterfly (wingspan 20-24mm) that, for its size, is probably one of the fastest. They are seldom seen except at flowers like this one, nectaring on Baccharoides adoensis on the Uve Trail. They spend most of their time in the canopy of savanna trees like Vachellia species, whirling around with the many tiny Blues that frequent such trees, their size making them almost invisible. They just seem to ‘appear’ on a flower, and just as rapidly, disappear! The upperside has a shifting green-blue iridescence that is very hard to spot because they seldom open their wings.

Boisduval’s False Acraea Pseudacraea boisduvali trimeni f trimeni male

Acara Acraea Tildia acara male

Here we have two butterflies with similar colours and markings. The Acara Acraea is smaller and flies with a slow, sailing motion as if he didn’t care if predators saw him. Boisduval’s False Acraea also sails slowly through the air. Both like to perch high on the edge of the canopy, wings open. Why the similar behaviour and colouring?

It has to do with predator deterrence. The Acraea’s bright ‘tutti-frutti’ colouring is aposematic, which is another word for ‘warning colouration’. He’s advertising that he tastes nasty – and it’s good advertising because his body is full of toxins that he absorbed from the host plant (one of the Passifloraceae) whilst he was a caterpillar. Slow flight is normal for distasteful butterflies because the wings-open posture reinforces the message.

The ‘False Acraea’ is just that. He’s not a ‘real’ Acraea. Although he mimics the Acara Acraea in colouring (except he’s a lot bigger and that further reinforces the message) and flight behaviour, if a predator ignores that and attacks him, he’ll drop the act and light the afterburners. If you look carefully at these butterflies’ bodies, you’ll notice that Acara Acraea has a slender body with a weedy thorax. The False Acraea has a robust body with a deep chest like a Charaxes – he’s built for speed.

Convolvulus Hawkmoth Agrius convolvuli female

When it comes to high speed lepidoptera you must look at the dark side. Moths have the edge on butterflies in this area, particularly the Sphinx or Hawkmoths. Convolvulus Hawkmoths are quoted as having a top speed of 100km/h over short sprints, and 50km/h over the long haul. And that’s quite a long haul – they regularly migrate from Africa to Europe in vast nocturnal swarms. It has all the hallmarks of a fast insect. Low profile, delta wings, and a massive deep chest holding powerful flight muscles. This moth has been mentioned in Leopard’s Echo before as having a similar power to weight ratio as a small bird. To power this high energy flight, they need high energy food – nectar.

African Hummingbird Hawkmoth Macroglossum trochilus

As well as these feats of speed and endurance, Convolvulus Hawkmoths do not settle to feed on nectar. They hover like a hummingbird in front of flowers with long corollas and capacious nectaries and penetrate deep into them with a proboscis (tubular tongue) that’s up to 120mm long. Most Hawkmoths do this; in fact, one of them is regularly mistaken for a hummingbird, to the point that it’s named after one. The African Hummingbird Hawkmoth even has a little ‘tail’ made up of body scales that can move up and down and help it to better control its flight movements. Most Hawkmoths are nocturnal, but the Hummingbird Hawkmoth is diurnal (day flying). Even Convolvulus Hawkmoths and other species may occasionally be seen flying by day.

Flight behaviour

We’ve looked at a few examples of different kinds of flight behaviour here. Like birds and bats, lepidoptera use wing flapping to power themselves through the air. Recent high speed photography techniques have helped scientists understand the aerodynamics of insect flight, and explain:

How a Charaxes can fly at speed and twist and turn in flight with enough agility to dodge Swifts and Swallows,
How Skippers and Sapphires (and many others) can take off vertically and accelerate to high speed in a split second, manoeuvring whilst doing so,
How Acraeas can soar so effortlessly without flapping their wings,
And how Hawkmoths can fly so fast and efficiently, yet hover as well as hummingbirds or kestrels?

To summarise – all insects appear to have similar flight mechanics and aerodynamics. Butterflies are particularly adept at rapid acceleration and changes of direction, as any butterfly collector can tell you!

The study of flapping-wing flight has been an area of intensive focus over the past 50 years, particularly for butterflies and moths. It’s been known since the early 1970s that their wings ‘clap’ together at the top of the upstroke beat, rather like doves and pigeons whose clapping is audible when they take off. When this clap occurs the air between the wings is pressed out, creating a jet, that pushes the animal in the opposite direction. What has been lacking are ways to analyse their wing movements and explain aerodynamically how butterflies and moths have such exquisite flight control and power.

Recent developments in high-speed photography, powerful and fast computers, ultra-lightweight powders with tight particle size control, and accurate laser illumination, have allowed the development of a technique called tomographic particle image velocimetry (tomoPIV). Essentially this allows the same kind of air flow pattern visualisation used in wind tunnels using smoke streams on model aircraft to be used on a micro scale on living butterflies. All this in a small container less than a cubic meter in size, and capable of image analysis by computer.

At this point I’m going to stop before I lose you all! For those engineers who are reading, or if you really want to be blinded with science, please access the references and links at the end of this article. They were the source of these images that help us to visualise what the scientists found.

Vortices created during wing flapping of a Large Tree Nymph Idea leuconoë as recorded using tomoPIV by Johansson and Henningsson (q.v.).

Vortices created during wing flapping of a Painted Lady Vanessa cardui as recorded using tomoPIV by Johansson and Henningsson (q.v.).

What they found was that the butterflies’ wings, being flexible and elastic with superb muscle control, are used to create motive power and control it exquisitely well. During each upstroke and ‘clap’ the wings form a cupped shape that generates a tiny rapid donut-shaped vortex, in the centre of which is created an effective jet stream. This thrusts the butterfly forwards. Lift is created by another, separate, set of vortices formed during the wings’ downstroke.

The image of the exotic Asian Large Tree Nymph (no relation to our African Tree Nymphs) is included because the vortices are more clearly visible. Its wingspan is more than 100mm. The Painted Lady is a common species found nearly all over the world including Africa. As I wrote this there was a major northwards migration of these in South Africa.

African Grass Blue Zizeeria knysna knysna flight sequence

Although they cannot capture those air currents, modern mirrorless cameras can shoot at 30fps and 1/8000s. This is a composite image of a tiny local garden butterfly taking off and flying. It shows the wing beat sequence well. This sequence only lasted about 1/10th of a second. The Canon R7 allows you to hold focus on a butterfly with the ‘first pressure’ on the shutter button that older cameras use to activate the autofocus. When the butterfly takes off, you squeeze the shutter button. Inevitably your reflexes are too slow to catch the take-off. But the sneaky camera was shooting electronically, blazingly fast, whilst your finger was on the button. The images were cycling through a buffer, the oldest ones being discarded – but the instant you squeeze that button, the last up to 50 images are saved. The lightning-fast autofocus keeps the subject in focus no matter how it dodges and weaves! Afterwards you can flick through them at leisure, choosing the ones you want to use. (Note – this isn’t a Canon advert – Nikon, Sony, Olympus, and others all make cameras that can do this. Isn’t technology wonderful!)

The triangular shape of butterfly and moth wings, the flexible and elastic nature of the chitin they are made from, and short, broad wings that are large in relation to the body, makes them masters of flight. Compared to a honeybee whose wings beat at about 200 per second their wingbeats are quite slow – but a Painted Lady can beat at 20 per second, and a fast Skipper probably 4-5 times that.

Far from being inefficient, weak fliers, they are masters. As well as generating power, the wings can create lift in the conventional sense as aerofoils, using wing-warping muscles to provide directional control as gliders do using ailerons. The two sets of wings are coupled using a mechanism under the insect’s conscious control and can be decoupled at will to allow air to escape from the surface. This allows them to avoid stalling in the same way that airliners do by using movable leading-edge slots or slats. This is how Acraeas and Sailers can fly so slowly with only minimal wing beats to propel them.

This kind of analysis is easier to achieve with butterflies, which are smaller and easier to image, than it is with birds. The findings of the research, however, appear to be applicable to birds. These discoveries are leading to the development of ornithopters, a term that will be familiar to anyone who has read Frank Herbert’s ‘Dune’ science fiction novels. The ones that have been built so far are tiny – 1.9g with a wingspan of 240mm, but they can fly for about 20 minutes using a tiny Li-ion battery. Spy cameras the size of houseflies that fly like them are not too far away…

References

Here are references to the some learned publications where I found this information.

Fuchiwaki, M., Kuroki, T., Tanaka, K. et al. Dynamic behavior of the vortex ring formed on a butterfly wing. Exp Fluids 54, 1450 (2013).

https://doi.org/10.1007/s00348-012-1450-x

Johansson L. C. and Henningsson P. 2021 Butterflies fly using efficient propulsive clap mechanism owing to flexible wings J. R. Soc. Interface.182020085420200854

https://doi.org/10.1098/rsif.2020.0854

Steve Woodhall is a butterfly enthusiast and photographer who began watching and collecting butterflies at an early age. He was President of the Lepidopterists’ Society of Africa for eight years, and has contributed to and authored several books, including Field Guide to Butterflies of South Africa and Gardening for Butterflies. His app, Woodhall’s Butterflies of South Africa, is described as the definitive butterfly ID guide for South Africa.

Steve has been a valuable and informative informal guide on many butterfly outings but recently qualified as a formal FGASA Field Guide and is now available to officially guide tours via his ButterflyGear business entity. Steve can be contacted on +27 82 825 8450 or steve@butterflygear.co.za