All aphids, both adults and nymphs, extract plant sap. Larger than aphids and whiteflies, spittlebugs may be up to 13 mm long. The brown, black, or gray adults are jumping insects which do not attract as much attention as the nymphs. Enveloped in a white, frothy mass resembling spittle, brightly colored nymphs suck sap from plants and sometimes transmit plant diseases. Only the nymphal stage of this insect family causes economic injury to plants.
Leafhoppers are fairly similar in size and appearance to the above spittlebug family.
Leafhoppers have the peculiar habit of running sideways, although when disturbed, adults will hop or fly away. Feeding on a wide range of plants, many leafhoppers transmit plant diseases or inject toxic substances into plants. Therefore, leafhoppers are capable of causing more plant injury than most sapsucking insects. Unlike spittlebugs and leafhoppers, treehoppers cause damage primarily by inserting eggs into plants rather than by extracting plant juices. The threecornered alfalfa hopper is one of the few treehoppers that damages agronomic crops.