The Giant Peacock: Europe’s Largest Moth

By Jose Luis Gallego, environmental communicator (@ecogallego)

Midnight walks in May, when the fields are bathed in spring moonlight, offer nature lovers some of the most charming moments in the countryside. Among the greatest surprises we might encounter are giant nocturnal butterflies, also known as moths. These lepidopterans share the same classification as diurnal butterflies and rival them in terms of the beauty and exuberance of their appearance.  

A gigant peacock in a tree

One look at the photo above, and you will see how true this is. What we see here is one of the most spectacular species: the famous great or giant peacock (Saturnia pyri), the largest moth or nocturnal butterfly on the European continent. It can measure 17 centimeters of wingspan, which is the end-to-wing distance.

Take note of the striking ocelli, or eye-shaped spots, on the wings: they are a survival tool that is as effective as it is surprising. It is an old evolutionary trick with which the great peacock manages to intimidate potential predators. The spots are in fact a tattoo of sorts, which the moth sports on its wings to suggest the eyes of an owl. They are meant to ward off potential attacks by nocturnal birds of prey that, misled by the ocelli, might mistake the moth for one of their own. 

Another distinctive physical trait is the plumage that adorns the head of male moths. They aren’t actually feathers but the male’s antennae: these sophisticated sensory organs play a fundamental role during the species’ mating season, because they allow the male to detect the pheromones of a female at a distance of up to ten kilometres. 

But the days of our beloved nocturnal butterfly are numbered, like those of all moths and lepidopterans in general. The butterfly is in fact the final incarnation of this spectacular insect; after spending time as a caterpillar, chrysalis, and imago, it finally becomes a moth. 
 

A gigant peacock in a branch

In the case of the giant peacock, this lengthy metamorphosis takes place over several years, but the lifespan of a moth comes to barely a week. At this point in its biological evolution, the moth’s only mission is reproduction: to lay eggs and die. The moth’s existence is so fleeting, it doesn’t even have a digestive tract, because it won’t need it.

During the final days of its life, our protagonist doesn’t eat or drink or go in search of a suitable place in which to establish its territory. Following the genetic mandate to complete its life cycle and bring new life into the world, the moth will spend the entire night flying about until it finds a tree trunk belonging to one of its preferred species where the moth then lays its eggs and dies. 

The giant peacock primarily inhabits deciduous mountain forests: from inland areas and coastal hills to the mountain ranges of the northern peninsula, where it is most frequently spotted. The moth has a particular preference for forests populated with beeches, willows, poplars and black poplars, and elms whose leaves provide the caterpillars with their food supply. Sometimes the moth will also lay its eggs in fruit trees, especially those of the Prunus genus.  

Adult moths mostly fly in May, occasionally until the first few days of June. Whatever the exact dates may be, no individual moth lives longer than a week. The moths lay most of their eggs towards the end of the month: females can lay up to 250 eggs. The little caterpillars begin feeding on the leaves of their host tree once they hatch, at which point they begin developing at a swift pace. 

Once the caterpillar reaches the appropriate size, sometime in August, it will have grown thick and long (up to 20 centimetres in length) and sport a startling bright green colour with ostentatious hairy blue protuberances. At this point, it will stop feeding and enter its next stage. This involves finding a safe place in which to curl up and spin a cocoon that will envelop the caterpillar completely. The chrysalis can halt its development (a mechanism known as diapause) in response to climate conditions, staying in the safety of its cocoon for up to three years until the weather is right.

Perhaps it is the ephemeral character of butterflies in general and the giant peacock moth in particular that makes these large “winged canvases” (as the great British entomologist Michel Chinery called them) into one of the most beloved creatures among amateur naturalists, myself included. With growing concern, admirers of the giant peacock have observed the serious and relentless population descent of these extraordinary creatures over the past few years. 

The use of pesticides and weed killers in cropland and forests has pushed a great many butterflies to their limit, so much so that many species have become a rare sight, the giant peacock included. It is increasingly scarce and difficult to find. Collectors are another factor that threatens its existence. This is why it is important to respect butterflies out in the wild and never, regardless of what our reason may be, capture, bother or chase them. Doing so might interrupt their reproductive process and thereby wipe out their entire incredible evolution, the prodigious biological effort of the metamorphosis described above.