As they mature, eggs become opaque white and develop a red ring. It is very difficult to find them on walnut trees. However, few other caterpillars are found inside walnut, pear, or apple fruit. The larvae pupate inside their cocoons in early spring, usually sometime in February or March. Shortly thereafter they emerge as moths.
Moths are most active from a few hours before to a few hours after twilight.
Each female deposits 30 to 70 eggs singly on fruit, nuts, or nearby leaves. After the eggs hatch, young larvae seek out and bore into fruit or developing nuts. After completing development they leave the fruit and drop from the trees to search out sites in which to pupate. Codling moth larvae feed within walnuts on the kernel. Nuts damaged early in the season drop off trees soon after damage occurs.