Mouthparts and gut contents of representative staphylinoid taxa were surveyed to discern four general patterns in the relationship between diet and mouthpart structure within putative monophyletic groups: mouthparts and feeding habits are similar among taxa (pattern 1); mouthparts among taxa are similar and feeding habits are diverse (pattern 2); mouthparts vary among taxa and feeding habits are similar (pattern 3); mouthparts and feeding habits both differ but are similar in some terminal taxa (pattern 4). Distributions of mouthpart structure and diet suggest that mouthpart construction does not necessarily constrain changes in diet when clades shift between predatorial, saprophagous, and sporophagous diets; but such shifts may be theoretically constrained by physiology or behavior. However, a shift from soft to hard or more compact food appears to be accompanied consistently by novel change in design, suggesting that morphological constraints limit this kind of diet.