I am growing strawberries in containers, like a strawberry pot. The flowers are fine, the fruit is nice, but when the berry is almost ripe, there appears to be small "tracks" of insect eating a thin layer. It looks like worm tracks, very narrow, but all along the fruit, even criss-crossing the berry. I looked on the leaves and plant for insects, but found nothing. What is it, and how can I protect the soon to be ripe berries? I do plan to get a netting to deter the birds.