It depends on the type of worm. Red wigglers are only a couple inches long, while European nightcrawlers can get up to about 8. It depends on how large your vemicomposter is, and how well you feed them.
The worms tht are found in composte heaps will be regular earth worms and they can grow up to around six or seven inches. They will be a pink in color and should have rings around them. Their length shoold not really be an issue at all. If having problems then cut out the light source.
When worm composting are done, the long of worms have difference according to their species. Generally, blue worms, earth worms, red wigglers are some species which can grow maximum of 4 inch.
