The need for a working key to aphid species in the genus Aphis has become apparent with the establishment of a suction trap network in ten Midwestern States. These traps catch many Aphis spp. and identification of these aphids is difficult. To fill this need we decided to begin a survey of the species in the Midwest and to begin compiling morphological data as well as host and distributional data for them. The genus contains over 400 species and so far we have over 50 species in our survey. Included in these are cosmopolitan pest species with wide host ranges as well as host specific native species. Some of the morphological characters that we are using are: number of sensoria on III, IV and V antennal segments, length of the longest hair of third antennal segment, number of accessory setae in the last segment of the rostrum, presence of lateral abdominal tubercles, presence of sclerites on the abdomen, color pattern of body parts (i.e.:coxa, siphunculi, cauda, and tibia). These have all been shown to be useful in discriminating among species in the genus. Morphological data will be taken only from specimens collected in Midwestern States. We are also interested in host plant data, as most of the native species feed on a limited number of host species. Our plan is to develop an interactive, web based key, and if possible a dichotomous key. Slide mounted specimens of all species are being photographed.