Leaving fallen leaves at the base of their horse chestnut trees, many French people have unknowingly become hosts to the next generation of a tiny insect known as Cameraria ohridella, commonly called the horse chestnut leaf miner. This small butterfly, measuring about 3 mm, was unknown to science before 1984. It was first observed near Lake Ohrid in Macedonia and later identified as a new species. Despite its small size, this insect has become a significant concern for urban and rural areas in France, where it has spread rapidly since the late 1990s. The leaf miner’s life cycle begins when its caterpillars bore narrow tunnels, or "galleries," through the leaves of horse chestnut trees. These tunnels, if numerous enough, can cover the entire leaf surface, turning it brown and causing the tree to shed its leaves prematurely in the summer. This not only affects the tree's appearance but also its ability to contribute to urban cooling and dust capture, according to a Swiss website on biological control. While the tree does not die from the infestation, repeated attacks can weaken it over time, resulting in smaller fruits and seeds. To control the spread of this pest, experts recommend collecting and removing fallen leaves from horse chestnut trees before the end of February. This is because the insect's chrysalises remain intact in the leaves during winter and emerge in spring. In urban areas, systematic collection is especially important, as the uncleaned leaves can recontaminate nearby trees the following year. FREDON, a French organization specializing in agricultural and environmental issues, emphasizes that this measure should be collective, involving both public and private spaces within a community. Proper disposal of the leaves is crucial. Composting is only effective if the pile reaches at least 40 °C for more than a week or 65 °C for a day, which is difficult to achieve with an ordinary open pile. Burning is not allowed for individuals, so the leaves should be taken to a local recycling center or green waste collection point. Local authorities can provide information on the best disposal methods and schedules. While the effectiveness of this approach has not been quantified by all sources, it is widely considered one of the most effective strategies to reduce the infestation's impact on the first spring generation of the leaf miner.