A Fluttering Moth Wreaks Destruction

By A. A. Wisley….

If, like me, you have watched many of the David Attenborough nature programmes you will have been amazed by the ability of the creatures around us to survive and prosper in what appears, to our eyes, as a dramatically difficult environment. One of these creatures is the Cyprus favourite, Thaumetopoea Pityocampa (TP), which has fashioned a life-cycle that makes it a very successful species; many might say, rather too successful.

Its life-cycle may be said to begin when the adult TP emerges as a moth from its underground pupa sometime in summer. Having an underground lair gives the pupa a good degree of protection to ensure that a decent population of adult moths will survive. It is likely that there will be many hundreds or even thousands of pupae in the same area so that many moths will emerge at the same time. Finding a mate should be easy. This is necessary, as the adult survives only for about 24 hours and in that period the female must mate and then find a place to lay her eggs.

Despite her short lifetime finding a suitable location to lay eggs is not be difficult for the moth as the pupa, from which it emerged, will be very close to its own, food abundant, “birth” place. The moth, however, may explore up to a kilometre away before laying up to 300 eggs on the needles at the top of pine trees. Bats are the only likely predator they will encounter.

It takes 30-45 days for the eggs to hatch out as TP larvae and during this period they are exposed to predation. Only small birds and insects such as crickets can get to their tree-top location. Several species of Tits do consume the eggs but, on the whole, Tits dislike coniferous habitats so their numbers are not as high as in deciduous habitats and consequently predation is lower.

Once hatched the larvae find themselves surrounded by high-quality food – pine needles – which they are adapted to enjoy. A juicy grub would, normally be a prime snack for any passing bird or lizard. However, these insects have developed a number of highly effective defences. First, they feed only at night, when most potential predators are asleep. Nightjars are known to eat them but whether many come to Cyprus I do not know. Second, they build a silken cocoon at the top of their tree which protects them from small birds and other predators. It also shelters them from the weather and extends their feeding season throughout autumn and winter. It is likely that most larva in a nest will be siblings making it a family home. Thirdly, these creatures protect themselves with a coat of urticating hairs, hundreds of thousands of them, which makes the larva indigestible to most birds and animals, the exception being a couple of species of Cuckoo. Their hair is highly irritant and can be dangerous to animals that inhale them or that get the hairs in their eyes.

Having fattened themselves on their hospitable pine tree and then grown into new and bigger skins 4 times, in early spring the caterpillars as a family descend from their tree and march off in a disciplined line to find a spot in which to burrow into the ground.  There they metamorphose into the pupa from which, after a month or so, the moth will emerge. Being buried 10 centimetres down gives great protection although birds such as Hoopoes, with their long beaks, will snack on them. If the pupa, somehow, feels that the climate outside is not propitious it may lie dormant in the soil for 2 years before the moth emerges. Another of Nature’s clever wheezes.

The TP is very successful. It has greatly expanded its territory but because its huge numbers are beyond natural control and are causing widespread damage to pine forests, especially in Europe it is regarded as a pest. The moth is spreading further north, year by year, and because its range expands with warmer winter temperatures it is seen as a reliable climate change marker.

Of course, the “blame” for its success lies at the door of we humans. Since agriculture was adopted in the Mediterranean region, 10,000 or so years ago, the ancient mosaic of forests have been cut down for fuel, buildings, pasture, and arable farming. In its place, garrigue and quick-growing pines have come to dominate as a type of natural monoculture. The normal diversity of trees, birds, other predatory creatures, and diseases that would otherwise control TP, has been suppressed making it easy for it to thrive and multiply with an ever-enlarging supply of pine forest food.

Ask, which is the greater pest? Mankind, the Habitat Destroyer or the Conquering Pine Processionary Caterpillar?