‘If we and the rest of the back-boned animals were to disappear overnight, the rest of the world would get on pretty well. But if the invertebrates were to disappear, the world’s ecosystems would collapse.’ – Sir David Attenborough
From a human perspective, there is much about invertebrates which can be hard to relate to, or even to conceive of at all. As mammals, our instincts likely count against them. It is no great stretch for many of us to empathise with an orang utan or a wildcat – but an octopus, or a lobster? Even the word “invertebrate” implies a lesser form of life, defined by what it lacks – a backbone.
Historically, perhaps the most high-profile invertebrate grouping has been the gigantic order known as Lepidoptera (butterflies and moths). These creatures are arguably quite well-known from a human perspective, by virtue of their appeal to our well-developed sense of sight. Their frequently bold and distinctive colouration has drawn our interest for millennia. One striking result of this interest has been the identification of approximately one hundred and eighty thousand individual species of butterfly and moth. For context, the total number of all vertebrate species known is below seventy thousand.
Sadly, amidst the ranks of described species of all kinds there exists a growing body of organisms which will never be seen alive again. One such is Sloane’s urania, a large moth formerly native to Jamaica. Though moths are often thought of as less brightly coloured than butterflies, this species was a glorious exception.
The large size and dazzling colour of these animals seems to have bought them to the attention of science quite quickly. The species was first described in 1776, being named in honour of the recently deceased Sir Hans Sloane, whose collection formed the basis of the British Museum. Whilst most moths are active at night, Sloane’s urania was a day flier whose beautiful wings served notice to would-be diurnal predators that it was, in fact, toxic.
Unfortunately, this moth’s natural defences would prove useless in the face of human activity. Surviving relatives of Sloane’s urania migrate periodically, after population explosions amongst their caterpillars defoliate certain areas. Consequently, their populations are not only subject to significant natural fluctuations, but they require multiple large bodies of suitable plants on which to feed. Interestingly, most adult moths do not eat at all, doing all their feeding at the larval stage and living only to mate once they emerge from their cocoons.
It is suspected that, during the late nineteenth century, when Jamaica’s lowland rainforests were being cleared for agriculture, one of this species’ key larval foodplants was lost. Urania larvae in general are picky eaters, feeding solely on a single genus of rainforest vine. Without a food supply for the next generation, extinction beckoned. Sloane’s urania was last reported in 1895 and is believed to have vanished entirely by the early years of the twentieth century.
Although six members of the Urania genus, similar in appearance and habits to Sloane’s urania, are still known to exist, this does not lessen the significance of the species’ loss. Indeed, the mere fact that Sloane’s urania is known to have gone extinct at all renders it hugely significant. Whereas it can be reasonably assumed that most of Earth’s mammal species are known to science, the same is much less true for other classes of animals, perhaps none more so than insects. Estimates of the total number of insect species stand at between six and ten million, of which around one million have been described.
The upshot of our continuing profound ignorance of so much invertebrate life is that no-one has much idea of how many species humans have driven to extinction. A 2005 study estimated that around 44,000 insect species had been driven extinct by human activity since the fifteenth century. More worrying still, in 2014 entomologists concluded that the total number of insects on Earth has dropped by about forty-five per cent since the 1970s. However, the number of documented insect extinctions in that time period stands at around seventy. Sloane’s urania is a rare insect indeed in that its passing managed to draw the attention of its nemesis.
Recent dramatic declines in bee numbers appear to have begun to alert humanity to the stupefying risk inherent in gambling with the future of invertebrate life on our planet. We would do well to remember that even the asteroid strike which ended the Dinosaur Age did not manage to cause a mass extinction amongst insects.