At the left you see the head of a mosquito. Of course mosquitoes are famous for being "flying syringes" as they fly about finding animals from whom they suck blood using their specialized mouth parts. In the picture you can clearly see the proboscis, the "needle" part of the "syringe." The antenna and palp help the mosquito feel. Actually, the proboscis is not nearly as simple in construction as a hypodermic needle. As the drawing at the left shows, the proboscis has a groove down its front inside which reside several extremely slender, sharp, saw-toothed stylets. If you ever watch a mosquito "biting" you, try to notice that the entire proboscis does not enter your skin. Instead, as in the drawing, its thick outer part, known as the sheath, bends, or "buckles," as the mosquito inserts its stiff stylets into your body. These stylets hold together in a way that allows blood to be sucked up.
The Leaf-footed Bug (family Coreidae) shown at the left also has sucking mouth parts. This picture is neat because it shows the held-together stylets outside the proboscis's sheath. In the picture the stylets are held together so closely that they look like just one. As with the mosquito, as the bug uses its stylets to cut into its victim (a plant in this case), the sheath bends as the stylets go straight into the tissue.
At the right you see a horse fly head, famous for its complex mouth parts that can cut right into a horse's (or human's) hide. Horse fly mouth parts are composed of nine different parts. At the right the dark item pointed downward in the picture's bottom, center is the horsefly's mouthpart. The cylindrical section pointing downward, the labium, wraps around the slender, sharp, swordlike parts that slash into flesh, cutting across blood vessels. When blood flows to the skin's surface, then the oval, spongelike thing at the labium's base sops up the blood and the blood flows upward through the labium. The brown, triangular item between the mouthpart and the antler-like antennae pointing at the picture's right side is one of two maxillary palps, which help the fly feel and possibly smell/taste what the palps touch.
At the left you see the head of a Large Carpenter Bee, genus Xylocopa. The honey-colored, wormlike thing at the bottom of the mouth structure is its "glossa," sort of like a tongue. The dark, downward projecting items right above the glossa are the "galea," and these are quite stiff and sharp. If you feel them with your finger you can understand how a carpenter bee can "chew" its way through solid wood, which it does when it excavates its nest-tunnels. Carpenter bees, however, being members of the Hymenoptera, are chewing insects, but you can imagine that with that wormlike glossa it can also suck a bit. Therefore this is one insect, like a number of Hymenoptera, that doesn't fit clearly into either the sucking or chewing category.
At the right the head of a female stag beetle, genus Platycerus, bears large, pincerlike mandibles that make this beetle look very dangerous. Most adult stag beetles feed on plant sap, so that doesn't explain why they have such formidable mandibles. Male stag beetles, who have much larger mandibles than the ones shown, sometimes use them while fighting with other males to establish dominance.
Look at the mouth parts on the paper-wasp head at the left. One glimpse is enough to assure us that this insect is not a sucker -- there's nothing looking like a tube. Those two overlapping, flap-like things at the bottom of the face are the wasp's mandibles. Paper wasps feed chewed-up insects of various sorts to their young, and when you see how powerful-looking those mandibles are, and note the toothed edges on them, you can imagine that this insect wouldn't have much of a problem chewing a nice, soft caterpillar. Though both wasps and bees are members of the Hymenoptera, you can see that there is considerable difference between the paper wasp's mouth parts, and those of the above carpenter bee. However, they are much more similar to one another than they are with, say, the curled up sucking-tube of the butterfly or skipper.