If you are concerned about staff:ratios report to Ofsted. You can do this anonymously if you like.
Too many nurseries are working under ratios or using too many unqualified staff and its got to be stopped.
To check, you could make light hearted conversation with staff, when you collect your child you could say is ......... in today? fill in gap with any staff that you don't see in the room, just to check that they havn't just popped out.
Yes biting is a phase, yes i had biters in my nursery and sometimes it would always seem to be one child they bit, cos they often played together. BUT it would never go unnoticed, we would speak to both parents sensitively and show them incident forms asking them to sign and then explain how we aim to stop the behaviour and what action plans we had in place. Normally this would include one-to-one work with the biter, especially at the times it tended to occur, this can be monitored through the incident forms and often happens at busy times of the day when staff are settin up the room etc So more often than not, the simple solution is to ensure the biter is kept busy at these times.
The nurseries curriculum should also be looked at to ensure it is an appropriate level to stimulate all children.
But please, if you think staff:ratios are not met, report to Ofsted, its illegal and not fair to the children.
Yes the nursery should cover sick leave, but many don't as agencies are expensive, and also the staff they send often may as well not be there. BUT if you have a manager and maybe a deputy manager sat in an office, they should be covering if their ratios are not up to scratch. I'm sure parents prefer their children to be looked after than paperwork to be done!
Hope this gets sorted for you.