Spring in the forest: Many insects, particularly caterpillars, hatch just when the trees' nutrient-rich leaves are still young and soft. This means they find a table laden with food and can start eating straight away. If oak trees are heavily infested by caterpillars in a given year, they react to this the following spring: they delay their leaf emergence by three days. This is unfavorable for the caterpillars. After hatching, they are literally faced with empty plates, because the oak leaves are still firmly hidden in the buds.