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What's happening to our conker trees?

Have you noticed whitish patches on the leaves of horse chestnut trees?  By the middle of summer, the whitish patches die and turn brown.  Sometimes there are so many that all the leaves turn brown, and it looks like autumn has come early.

We need your help to discover more about natural pest control of the leaf miners.

Our conker trees are under attack by 'alien' invaders!

The damage is caused by a tiny 'alien' species of leaf-mining moth, which has spread across much of the UK since 2002. The moth’s caterpillars eat the leaves from the inside. Infected trees are weakened, and produce smaller conkers.

Fortunately, there may be help at hand. Some of the leaf-mining moths are attacked by natural pest controllers, in the form of tiny insects (called parasitoids). These insects lay their eggs inside the caterpillars of the leaf-mining moths, and their larvae eat the caterpillars, eventually killing them.

Take part in citizen science!

Back in 2010, about 2,000 people took part in a citizen science study on the leaf-mining moths and their pest controllers and the results were published in the scientific journal PLOS ONE. We found that pest controllers were present - but the numbers were too low to control the leaf miner.

Now, in 2020, we want to discover what has changed over the decade: have the numbers of pest controllers stayed at a low level, or are they increasing? Once again, we cannot do it without you - so take part in the Mission: pest controllers!

Mission: pest controllers

Between 4th and 13th July (inclusive)

  1. Pick a leaf from a conker tree that is infected with leaf miners.
  2. Seal it in a bag (a ziplock food bag is ideal), so even tiny insects cannot escape.
  3. Keep it somewhere cool for two weeks.

Between 18th and 24th July (two weeks later)

  1. After two weeks, the insects inside will have hatched out.
  2. Count the moths and the natural pest controllers, and send us your results. (Instructions for sending result will be available on 18th July.

See the full instructions and sign up to receive more information, reminders of how to submit your results and information about our brand new forthcoming project Nature Up Close & Personal.

Interested in a new project to discover more about our connections to nature?

From 14th July, you can also take part in Nature Up Close & Personal: A Wellbeing Experiment. It's an investigation into the activities that support our connectedness to nature and our wellbeing. We'll give you short nature-based activities to do over the course of a week and ask how they made you feel. Together we'll be able to find out more about nature and our wellbeing.

Interested in discovering more about citizen science?

Read our guides to environmental citizen science, produced with UK Centre for Ecology & Hydrology and partners. Find out more about species recording at the Biological Records Centre.


This project supports the United Nation's International Year of Plant Health.

Damage to horse-chestnut leaves

The horse-chestnut leaf-miner
(Photo: Rich Andrews)

Collect leaves like these to find out more about the
alien moth and the pest controllers
(photo: Rich Andrews)