Citrus leafminer (Phyllocnistis citrella) is a very common pest on citrus plants. The adult is a small moth (wingspan approximately 5mm) which lays eggs on flushes of new growth. Tiny grubs then hatch and burrow into the leaf.
The larvae feed by tunneling their way around leaving tracks or mines (hence their name) all over the leaf. These tracks commonly look like silvery wobbly lines but may also look like a blister on the leaf. Leaves usually become quite distorted and curl up as the larvae start to pupate.
Read more here.