No see 'ums are larger than chiggers (red bugs) and they bite-we call them flying mouth parts. If you think they are not as bad as chiggers, you need to come spend a weekend at my place at the beach here in North Florida. They are murder, just in a different way. Breezy days keep them at bay though. The big difference, is their agony lasts 24 hours at worst-but while they are chewing on you, it sucks - I keep my hair very short and they will chew on your head too if you have short hair. Chigger's give their gift for a while. I prefer no see 'ums to chiggers, cause you know they are biting you and can at least get away from them. Regular screens do not stop them, it needs to be very small screening to keep them out. Thermacells work on no see um's too.
They both suck.