The categories are pretty course, but that is a deliberate choice and I understand that thought has gone into it. As I was originally recruited to this site iSpot was designed to be the ‘friendly uncle’ who takes a budding naturalist out and shows them things. So necessarily the categories were set at quite a high level - if you are just beginning you might know the difference between a fly (diptera) and caddisfly (trichoptera) so if before you could contribute you had to work that out it would be off putting. Actually I get the impression (subjectively rather than based on real evidence) that even the current ‘invertebrate’ category causes confusion with a lot of new people putting stuff down as ‘other organism’ rather than one of then inverty-thingummies.
A similar reasoning was behind the choice of only a limited number of habitat types.
Early on I suggested that the iSpot reputation system should allow you to lose reputation for getting stuff wrong as well as gaining it for getting it right. In the real world that is how it works, both getting it right and not getting it wrong matters. iSpot deliberately chose not to do this as they had a philosophy of nothing negative happening to people (again to encourage people just venturing into natural history observation) and losing reputation points would count as negative. That argument has a lot of merit.