It depends on the kind of wasp you have. Paper wasps eat nectar and other insects including caterpillars and flies. Cicada killer larvae feed on cicadas and other insects. Adult cicada killers will feed on flower nectar, fermented sap from trees, and other large plants in their habitat. Adult mud daubers feed on plant nectar, honeydew, and body fluids from the spiders they capture. Some species of mud dauber even feed on dangerous black widow spiders.