Absolutely Conkers

A horse-chestnut tree leaf with the typical markings of miner moth Cameraria ohridella

Rejoice, for it is that time of the year once again, when the horse-chestnut trees are fully loaded with their shiny deep red bullets and conkers fall from their tired branches onto our heads, before rolling on the wet ground and bouncing gracefully over a bed of brown leaves.

We have spent quite some time observing and filming these trees recently, and our collection of conkers is starting to take over the house. It is sufficient to say I have even found conkers rolling through my bedsheets as I went to sleep...

As we followed the browning of the leaves and the falling of the conkers, we couldn't help but worry as we observed the destructive work of the tireless horse-chestnut leaf miners (Cameraria ohridella). These are very small moths that on the larval stage feed on the tree leaves, burrowing or mining their way through the green, and leaving streaks of brown destruction on their path.

Holding strong against the assault of miner moths

Once the caterpillars grow to full size (which is a mere few millimetres), they cocoon and emerge as micro-moths, which we could observe in millions during the past weeks, flying around the sad looking trees and shrivelled up leaves. These parasites are not lethal to the trees, but they cause their premature ageing, meaning the horse-chestnuts that are infested tend to shed their leaves and conkers as early as the end of August.

A quick search for these leaf-mining caterpillars and we discovered that they were first observed in 1984 in Macedonia. Since then, they quickly colonised new trees and new countries, and they are currently found living and thriving on horse-chestnuts of most European countries. As far as we could observe, every horse-chestnut tree in Bologna is affected but, to our surprise, when we inspected some trees in Hamburg a week ago, we couldn't find trace of their presence. The leaves of these healthy trees were still radiant and green and the chestnuts were strong, big, and heavy, still dangling from the branches.

A freshly fallen conker, in all her shiny and smooth beauty

But it looks like apart from a few healthy trees in northern Europe, the moth is spreading, and there isn't much we can do about it. What this means is that we'll have to get used to smaller and earlier conkers, and that rather than being a typical autumnal event, we'll have to get used to seeing conkers rolling at our feet as we walk back from the beach, at the end of summer. It's good news for the little birds though, as we found blue, great and coal tits, as well as black birds and thrushes, literally feasting on the larvae at the top of the trees. A welcome and hearty snack in preparation for the long, rainy autumn that will soon arrive.

Not the healthiest leaves, but still attractive in the first light of dawn

Nick, Oropendola Productions