This time of year it looks like someone has visited every other Sugar Maple (and to a lesser extent, Red Maples and birches) leaf with a hole punch. The Maple Leafcutter Moth (Paraclemensia acerifoliella) is the hole-punching culprit. At the beginning of the summer, leafcutter larvae hatch and begin mining tissue between the upper and lower layers of maple leaves. The mines are barely discernible, as the larvae are so small at this stage. A bit later in the summer the larvae start using their mandibles to cut out round discs of leaf tissue. They take two of these discs and fasten them together with silk, forming a protective case around themselves as they consume additional tissue between the leaf veins. It is this feeding that causes the “punch holes.” As the larva grows, it cuts larger and larger discs to form its case.
When September comes, the larvae are mature and descend to the ground, carrying their homes with them as they move into the topsoil to pupate. Orange-headed, metallic blue-winged adult moths will emerge in the spring, leaving their leaf homes behind.
Because leaves have produced most of the sugar they are going to produce by late summer, the feeding behavior by the moth larvae that occurs from August until leaf fall isn’t a threat to the health of the tree unless complete defoliation occurs for three consecutive years or more.
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