One of the side effects of keeping greens growing all winter under a row cover is that not only do the plants survive, other things survive as well!
I went to pull out all the old spinach plants yesterday, and they were covered with aphids. The spinach was really past using since it was getting bitter, and a good thing too. The plants were almost slimy with aphids when I pulled them. You can see from this picture that some of the aphids have wings, which will allow them to go find new places to feed and multiply. (Oh goody!)
An infestation this sever would definitely warrant some sort of spray if we wanted to keep it going. Probably a neem oil or pyrethrin would be the product of choice. (Honestly, the spraying should have been done right when we took the row covers off, before the aphid population exploded!) I just pitched the whole mess into the compost bin. Probably not the wisest choice, but the winged aphids were going to go their merry way no matter what I did.