Too many svchost.exe instances in my Task Manager

Hi everybody!
Lately I noticed that I have too many processes in my task manager. And I found that there are 10 processes of svchost.exe and they eat up an unusual amount of memory. 4 of the processes are listed under Local service 4 under system and 2 of them are under network system.
Is this normal or do I have a virus? If so what can I do about it?
Thanks in advance.
