Aphids are common insects to see in field crops, especially in alfalfa. In Iowa, there are at least four different aphid species that can develop on alfalfa (Table 1). A recent report of cowpea aphid near Gibson, Iowa from extension field agronomist Mark Carlton prompted me to write this article. Many of you are quite familiar with pea aphid, but other species occasionally show up alone or in combination. Learning to distinguish the aphids takes a little practice with a hand lens, but is worth knowing in order to make sound treatment decisions.