Yes, you need to take your kitty to the vet!

That wound needs to be checked, debrided, etc., etc. Hope it won't be too serious...but I wouldn't wait any longer... Your cat is probably quite uncomfortable. You will be surprised how much they tolerate... It looks like an open wound with maybe a maggot or two living in it. Maybe you kitty got bit there by another cat or something? If that is a maggot, that wound has been there for a while...
Anyway, you probably want your kitty to be on Frontline regularly to prevent tick bites in the future. Those ticks do carry nasty diseases, and it may danger humans, too...
I hope it will be taken care of it soon~~~ Good luck!