There are over 10,000 species of grasshoppers (Acrididae) that are differentiated by climate, location and plant feeding preference. Some species are specialists on grass; some are specialists on forbes; and some are generalists feeding on both grasses and forbes. The chewing mouthparts of the grasshopper, the mandibles, have different adaptations to the different plants groups*.
The mandibles of all grasshoppers are asymmetric, with the left overlapping the right when the mouthparts are closed. The lower part of the mandible contains the edge used to cut plants into pieces small enough to swallow. The cutting edge often incorporates zinc or other metals to increase its hardness and make a sharper edge. This edge is differentially adapted in forbe and grass feeders.
In forbe feeders, the mandible has jagged teeth, similar to a serrated knife. The mandibles “punch” a leaf piece from the edge when they close. In grass feeders, the cutting edge of the left mandible resembles a smooth knife blade. The “teeth” are closely apposed and separated by only a shallow grove. In some grass feeding species, the teeth form a smooth cutting surface without grooves. These mouthpart adaptations can limit the ability of some grass feeders to effectively feed on forbes.
*Isely, F. B. 1944. Correlation between mandibular morphology and food specificity in grasshoppers. Ann. Entomol. Soc. Am. 37:47–67.