How do butterflies do it?

Graphium Agamemnon, tailed jay.

A late safari at the grove today. Bright and sunny so lots of butterflies around, probably as many as ten species identified.

The tailed jay has already been featured twice this month, but I thought I would examine another aspect of this stunning butterfly - feeding.

Unless the flower head is large and stable enough to land on and support this heavy butterfly, then photographic capture is very difficult as the wings are in constant motion.

In today's blip, the jay is feeding on a creeping foxglove, asystasia gangetica, a small, delicate flower head. Only one, sometimes two blooms per plant open and are spent by mid afternoon when the petal bell falls off. If the butterfly were to try to land on this flower, the bloom would simply fall off.

The butterfly lands lightly, gripping the bloom for stability and flaps its wings to support its weight while feeding. Only a second or two per bloom so you have to be quick.

The odd thing is that the butterfly only flutters its wings no more than 10 degrees from the vertical, but somehow this is enough to give the butterfly sufficient lift to support its weight. It is clear to see that the distance from the stem to the center of the butterfly is quite considerable and if there was no lift from the wings, the bloom would bend from the leverage of the offset weight.

Most people would think that butterflies achieve flight by pushing down on the air with its broad sail like-wings, just like you think that you do when you are pushing the water back when you swim. In fact, in both cases, this is not true. In this case, at no time are the wings moving downwards, so obviously the pushing down theory is immediately dispelled with.

In the case of the butterfly, the wings start off closed at the vertical. When the wings are pulled apart, a vacuum or low pressure is created and it is this that sucks the butterfly upwards.

All butterflies use this method to become airborne but then resort to a different theory for general flight, which I will talk about another time. Some butterflies do use this theory for general flight, like the sailors, Neptis duryodana for one example. You can tell because they flap once and then glide, the single flap every second or two enough to supply sufficient upwards force to maintain flight. They are masters of the air currents and I have witnessed glides of up to 30 meters from a single flap, given a gentle breeze.

As for swimming, as the arm is pulled through the water, a vacuum or low pressure is formed on the back of the hand and arm, it is this that pulls you forward.

"sorry, I don't believe you" I hear. Well, that's allowed, it is called having an opinion and we are all entitled to a few of those. Consider a ball and a plate the same diameter. The ball slips through the water with relative ease but the plate (face on) requires considerable effort to drive through the water.

The water is able to slip around the shape of the ball, just like the aerodynamic shape of a wing, so very little vacuum or low pressure is created, whereas the flat plate creates a large low pressure which pulls in the opposite direction to what you are trying to pull.

I have tried to keep it simple, avoiding all the big words that I wanted to use. I doubt that you will be convinced either, as this took me, as an engineer, a long time to grasp and accept.

Something else that I will talk about in the future - ever notice how the best, world class swimmers seem to move their arms slower than the also-rans?

Also, ever notice how the swimmers arms jiggle from side to side when pulled through the water? Try it next time you are in the pool. If you report back, I will explain it.

Dave

Blipping will be sporadic over the next several days, as I will be on a road trip.