Various creatures do like to live under decking and sheds.I built a shed withg a suspended wooded floor and I regularly get rats under it. If I was to do it again I'd put in a concrete or patio slab base

Obviously you'd need to sort the drainage issue first .

as the 3 species of native snake are pretty special and only the adder/viper is venemous [then it would rather slither away than attack] Iwouldnt worry about them. I d be more concerned about rats living underneath. You can put a mesh down that is supposed to stop them getting underneath.

thankyou for your help.another question,how deep do i need to dig the footings,on boggy ground

thankyou again

If it is only a very lightweight structure I'd suggest 12-18 inches if you're just going around the edges but ofcourse it depends entirely on soil makeup,how boggy it is and other factors.

To be honest on a typical lightweight shed a couple of inches of concrete laid on 3 inches of gravel over the full area of the building should do the trick. Make sure the top of the concrete is above the water table and I'd lay a piece of builders ploythene between the concret and the gravel to make sure water cannot seep through.

It may crack or subside a bit later but unless it is a particularly fanct summer house it wouldn't matter.