Now here’s a thing I hadn’t seen before – a very large webbed nest up high in an Aleppo pine tree. Was there some form of large spider building these? For there were three similar to be seen on the same tree, each one about the size of a rugby ball or football.
When we got home, I looked it up, and these silken nests are built by Pine Processionary caterpillars. They spend their days inside the webbing, venturing out at night to feed on the pine needles. A good-sized colony can strip a tree over the few months they’re in residence and they’re considered a pest in many places. Although they’re named for pine trees, they’ll also be happy to munch on larch trees or other conifers.
The Pine Processionary is most famous for its next stage of development, when the fully-grown caterpillars all descend from the tree and march off in a long line to find somewhere suitable to pupate. This part of the process we’d also recently witnessed, over by the Glavice headland. The processions can get really long, each one following exactly where the one in front goes. A famous experiment by French entomologist Jean-Henri Fabre had them going round in a closed circle for weeks!
The latin name for these hairy creatures is Thaumetopoea pityocampa and it’s important not to touch them, for those hairs are extremely irritating to humans and other mammals, in some cases causing a serious allegic reaction. When I was looking for information, the first website I found was full of dire warnings about these pests and how to eradicate them from your garden without touching anything – and certainly don’t allow cats or dogs to go near them! Yikes!
Pine processionary caterpillars
The final, completed stage is the Pine processionary moth (PPM), that only lives for a single day – which they obviously spend mating and laying eggs. Given that they’re considered a pest in terms of defoliation of trees in Southern Europe, it’s probably just as well they don’t have much time to spread very far or very fast. The image below is courtesy of Wikimedia Commons, as we haven’t seen the actual moths.
Thaumetopoea pityocampa – the Pine Processionary moth
On the positive side, the Pine Processionaries (at various stages) are food for several birds and bats, as well as hosts to solitary wasps. And on an island like Hvar, it’s a natural part of the environment and doesn’t appear to do much damage. Himself remembers much longer chains of these caterpillars when he was growing up near Rovinj in Istria. So long, he says, that he got bored looking for the end!
Read more
Wikipedia article on Pine Processionary moths
Forestry Commission (UK) assessment of the Pine Processionary threat to trees
Go Hvar 
We have a kind of these here too. They can completely defoliate a huge Australian cedar tree.