When to look for OPM
Spring and summer
The OPM caterpillars emerge from late March to May. They will move down the trees as they get older and bigger, and build nests.
From late June to early August, the caterpillars retreat into the nests and form a pupa (cocoon). The pupae remain in the nests until they emerge as adult moths.
Autumn and winter
In winter the nests are easier to spot when there are no leaves on the oak tree or on the ground, but you can find them at any time of year.
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