If you find large white grubs in the soil of your potted plants or your garden, they are likely the larvae of the Green Fruit Beetle.
Read more about these
white grubs. See
more photos.
These larvae are usually found in compost piles where they eat decaying matter and are considered beneficial, but they are not good to have in a potted plant since they will likely eat the roots. It is a good idea to sift through the soil in the pot to remove (and discard) and then repot the plants into fresh soil.