When you open a pea pod, some of the peas have dark excrement near them. Inside infested peas you will find a tiny light gray to brown caterpillar.
You can use row cover (garden fleece) to prevent egg laying by adults if pea moths are a serious problem. Early planting also can help peas escape damage. In most areas of Europe, natural predators help to keep this pest under control, but this is not the case in Canada, where the pea moth has become a serious pest. Flat-podded snow peas are less affected compared to shell peas.
Check plants regularly as soon as they begin to bloom, and pick off affected pods. Little can be done once the adult moths have laid their eggs on pea plants.
In large plantings, pheromone traps are often used to monitor this pest.