sounds like springtails (Collembola) to me
http://www.wormcity.co.uk/wormfaq.htm#springtails
don't worry they won't harm your worms, they are all part of the living ecosystem - that is your wormerySpringtail's - Springtail's are small wingless insects that jump when disturbed, they have a small spring-like structure under the belly that catapults them into the air. Springtail's feed on fungi. - aids composting
Ronnie