Conker season is in full swing, but scientists are worried that the little brown nuts might be a bit smaller than usual this year.
Conkers can be found growing on horse chestnut trees during the autumn here in the UK.
However scientists think they might be a bit smaller this year because of a bug called the leaf-mining moth.
The moths lay their eggs on the horse chestnut leaves.
When they emerge as a caterpillar they eat the green stuff inside the leaves of the tree.
This causes the trees a lot of stress and can make them weaker and more likely to catch diseases.
Leah has been finding out more about how to protect the trees.