You hear a humming sound- is it a bird, is it a plane? At the risk of sounding frivolous it is difficult not to get excited at the sight of one of these astounding creatures. From a distance you would be forgiven – and this is no accident – if you thought that a host of hummingbirds had alighted in your garden. However, closer inspection would reveal a surprising lack of avian characteristics and you would be forced to re-assess the situation. With no legs or claws – and certainly no beak what you have here is a moth. No ordinary moth either – just take a look at that tongue. In truth, it isn’t actually a tongue. You may well ask, then, if it isn’t a tongue, what on earth is it?
There aren’t many – if any – tongues that can do that and it has a different function. What that amazing body part is called is a proboscis. That is the name given to an extended appendage from the head of an animal. This elongated organ is for sucking (more about that later) and it is also known as a haustellum. It is made up of two tubes that are held together by hooks. Strangely (and even scarily) enough these tubes can be separated – unhooked – when the moth needs to clean it. Each tube is concave on the inner side and this means that when they come together they form a central tube – and this is what the Hummingbird Hawk Moth (Latin name Macroglossum stellatarum) uses to suck up pollen as well as moisture.
How is the suction actually made, though? This is where the physiology of the hummingbird gets a little more bizarre. It has a sac in its head and it contacts and expands this sac. When this happens the suction simply happens. Most Lepidoptera (the order of animals in which both moths and butterflies belong) have this type of proboscis. Some though, do not have mouth parts at all and so do not feed in the imago (the adult form). There are some though that have mouth parts which are used to chew. The Hummingbird Hawk Moth, though, uses its proboscis – and it is a hungry insect indeed.
Yet don’t moths come out only at night? That is how we usually think of moths but many species are diurnal (which means they go out in daylight). The Hummingbird Hawk Moth goes out at both dusk and at dawn but it is regularly seen flying around during the day, particularly when the sun is shining brightly. What is a little different from other moths is that it will not avoid rain and is quite happy flying during a spell of aqueous precipitation, unless it is too heavy. It has been studied a great deal and it seems that this species of moth has a pretty good ability when it comes to learning colors – important so it can get to its favoured food sources.
Just when you think you have seen the photograph with the proboscis of the Hummingbird Hawk Moth as fully extended as possible, there comes another which shows it stretching out just that little bit further.
So, where do you go to catch a glimpse of this wonderful moth? It is to be found all over the Old World, from the coast of Portugal to the islands of Japan. It doesn’t extend very far north as it likes a warm climate but during the summer months it can be found throughout the hemisphere. As it is migratory it will leave the colder northern areas and retreat towards the south – it would not survive the Winter anywhere north of the Alps of the Caucasus. Another family of moths, which are locally called Hummingbird Moths can be found in the United States but these are referred to as bee moths in Europe.
Many people think that imago moths will produce a single batch of eggs and then flit away somewhere to die quietly, their function performed. Not so the Hummingbird Hawk Moth, which will produce at least two broods of eggs in a year – in fact it will lay up to four sets of eggs in a year. It does not hibernate but it is much less active in the colder seasons. It overwinters where it can find a nook or cranny – among rocks, trees and even buildings. If there is a particularly warm day during the winter it will come out and feed.
It lays its eggs singly. Its caterpillar – at first yellow – become a rather regal looking green as it heads towards it pupa stage. Pale and glossy, the green eggs have a diameter of only a single millimeter. They resemble the buds of the host plant Galium and take up to eight days to hatch, camouflaged as they are to look like part of the general greenery. The female will lay anything up to two hundred eggs, each on a separate plant – a very tiring business no doubt.
With two grey stripes, each with a creamy border and a purply red horn at the end to frighten off would be attackers the larva feeds itself at the top of the host. This stage can last as little as only twenty days – depending on the warmth – and then the caterpillar will be ready to pupate. When this happens they do not thread themselves on to the plant but drop to the soil and detritus at the base of the plant. Hidden there, they will hopefully emerge safely as the imago. It has evolved, at this stage, to look like something that nothing would want to eat!
The adults love flowers with an abundance of nectar. These include Buddleia, Nicotiana and Phlox. The adults do not feed aimlessly, either. They have been seen to trap-line. That means that they return to the same plants at the same time each day. Without the help of the Hummingbird Moth many of our popular garden flowers would not be pollinated. The proboscis has developed over time to its current length as the flowers which attract it the most have long, tube-like organs containing their nectar. Evolution loves necessity – it most certainly is the mother of invention.
So why do these moths look – and act like real hummingbirds? Scientists think that this may well be a case of convergent evolution. This is when an identical biological trait is acquired in completely unrelated lineages. This can happen when two species occupy a similar or the same ecological niche – one that demands a distinct way of life to facilitate survival. Birds and bats would be a fine example. However the flying action of the Hummingbird Hawk Moth came about, one thing is sure: the sight of one as it goes about its business of feeding is one that is never forgotten.