Insect mandibles are a pair of appendages near the insect’s mouth. Their function is typically to grasp, crush, or cut the insect’s food, or to defend against predators or rivals.

Grasshoppers and Crickets

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The mouthparts of orthopteran insects are often used as a basic example of mandibulate (chewing) mouthparts, and the mandibles themselves are likewise general in structure. They are large and hardened, with cutting surfaces on the distal portion and chewing or grinding surfaces basal. Large pieces of leaves can therefore be cut and then pulverized near the actual mouth opening.

Beetles

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Nearly all adult beetles, and many beetle larvae, have mandibles. In general form they are similar to those of grasshoppers: hardened and tooth-like.

Beetle mandibles show a remarkable amount of variability between species, and some are very highly adapted to the food sources or other uses that the species has for them. Certain firefly larvae (family Lampyridae) that feed on snails have grooved mandibles that not only physically break down their prey, but also deliver digestive fluids by these grooves. Ground beetles (family Carabidae) of the tribe Cychrini have long mandibles that project far in front of them, which aid them in feeding on snails inside their shells. Members of the stag beetle family (Lucanidae) have greatly enlarged mandibles that are often forked, resembling the horns of various deer, from which their common name comes. Males use their mandibles to grasp each other as they compete for mates.

Ants, Bees, and Wasps

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Most adult Hymenoptera have mandibles that follow the general form, as in grasshoppers. The mandibles are used to clip pieces of vegetation, or to disassemble prey.

True Bugs

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The Hemiptera, and other insects whose mouthparts are described as piercing-sucking, have modified mandibles. Rather than being tooth-like, the mandibles of such insects are lengthened into stylets, which form the outer two parts of the feeding tube, or beak. The mandibles are therefore instrumental in piercing the plant or animal tissues upon which these insects feed, and in helping draw up fluids to the insect’s mouth.

Flies

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Several families of flies, notably mosquitoes (family Culicidae), have mandibles that are modified into stylets for piercing, similar to the true bugs.

Flies of the Muscomorpha, including the house fly, Musca domestica, stable fly, Stomoxys calcitrans, blow flies (family Calliphoridae), and many others, lack mandibles altogether.

Butterflies and Moths

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All but a few adult Lepidoptera lack mandibles. The exception is the mandibulate moths (family Micropterigidae), which have fully developed mandibles as adults.

Thrips

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Thrips have a variation of piercing mouthparts. In this order only the left mandible is present, modified into a stylet.

Beetles