I cannot say all that much about them. Until recently, this and four other species (maverlius, smaragdinus, inundatus, diluvialis) were considered one species. Now there are keys available that can morphologically separate all these species in most life stages (but this is still difficult!).
This species complex (or some members thereof) are the premier vectors of malaria in the Eastern US and Canada (I say are because cases of "airport malaria" still crop up).
Like many mosquitoes, getting these to species without the specimen in hand with a scope and a key is tough. Getting Anopheles to genus should be easy enough on sight, once you have seen a few specimens and observed their characteristic postures. IDing a specimen to quadrimaculatus group should not be too hard if you have smacked the bug and have a handlens at least. The only way I know of to achieve even this is to key out many pinned specimens and memorize the key features.
Here is a link to a PubMed reference that discusses the morphology of the group http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9474550&dopt=Abstract.
Keys to every species of mosquito in North America (except Mexico) are found in Darsie and Ward 2004 (1)
I will try to go through my refs on Monday to get you a better synopsis on this species.