Spring is starting to make itself felt and this is the time when you will see the emergence of some very odd-looking eruptions from the base of bamboo.
Subterranean alien invasion it is not, it is simply this year's new canes thrusting themselves in to existence. These new canes will grow at an amazing rate, even in our milder climate they can grow from ground level to 3m within a month or so.
New canes can be removed if unwanted, but best practice is to allow them to grow and remove older canes in their place. As a rule newer canes are more impressive than older canes and should ideally be kept.
If you want to reduce the height of a new cane wait for it to finish growing, to harden and for it's new leaves to emerge then it can be safely pruned.