These are probably pot worms (enchytraeids). They do a similar job to brandling worms and are nothing to worry about; you find them in most worm bins. They are very tolerant of waterlogged/acid conditions so if you find them proliferating, and your worms are getting fewer, improve the drainage. Mixing in some shredded newspaper will help. You can also add a sprinkling of calcified seaweed or rock limestone (dolomite) to correct the acidity. Newly hatched brandling worms are also whitish and only half an inch long. You can distinguish them from pot worms by their blood vessel which gives a pinkish tinge.