Multiple factors contribute to the significant challenge of obtaining an accurate assessment of infestations of spider mites under field conditions in field crops and trees. In addition, standard practices for counting spider mites do not provide a historical record of individual numbers. We developed and evaluated a new device, the “leaf inspector”, for sampling spider mites. Adhesive tape was pressed toward the underside of leaves of maize, Zea mays L., and spider mites on pieces of tape were counted later with the aid of a stereoscope (16–25 magnification). Sampling spider mites using the leaf inspector in the field required 30–60 seconds per leaf, and subsequent counting of spider mites with the aid of a stereoscope required 8 minutes per piece of tape. We showed that: 1) absolute numbers of spider mites on maize leaves were positively correlated with those obtained with the leaf inspector, 2) leaf dimensions did not significantly affect performance of the leaf inspector, and 3) a residual but fairly constant percentage (about 20%) of spider mites was left behind after a maize leaf had been sampled with the leaf inspector. Thus, a more accurate estimation of spider mite abundance was obtained by adding 20% to each count based on using the leaf inspector.