Basically, all insects have segmented bodies divided into three parts, the head, thorax and abdomen. Insects also have two pairs of antennae and three pairs of legs. Without these 3 body sections, 6 legs and 2 antennae, the animal in question is not an insect! This is why spiders, centipedes and worms, often considered by the layman to be insects, aren't such at all.
Some insects do not have wings at all. The order Diptera (flies, including mosquitoes), only have one pair of wings. Most other winged insects have two pairs, and that applies to virtually all the bees and wasps covered in this website.
The head, of course, comprises of the insect's eyes and mouthparts. These vary widely. Some insects can bite and chew, some can only use a proboscis (long, coiled tube; you can compare this to a drinking straw!) to take in nectar or liquids; some insects don't feed as adults at all! Insect vision also varies; some are virtually blind, while others have excellent, 3D vision. Mantids and dragonflies are said to have the best vision of all. Bees and wasps mostly have a pair of strong, stout mandibles, used for biting prey or nesting material. Most bees also have a long tongue which they use to drink nectar. Most wasps, although they do drink nectar, have a shorter tongue, and therefore cannot reach into deep flowers. Bees and wasps have good eyesight, compared to many other insects.
The thorax is the central linking point for the insect's legs and wings; it contains all the muscles needed for the insect to move. The abdomen usually contains the insect's digestive tract. Also, insects do not have lungs. They breathe through tiny holes, known as spiracles, located on the underside of the abdomen.
In actual fact, these three basic parts of an insect can be broken down into many individual sections. Although these are of utmost importance in scientific texts, they will hardly be used here, since there is no need to; this site is one designed for everyone, and there is no need to overly complicate things. The parts below are some of the important ones that are good to learn just for reference.
In many bees and wasps, the abdomen comprises six segments. You will frequently see these referred to as the gastral or abdominal segments. These segments are actually made of two sets of plates, one above and the other below. The scientific term is for the plates making up the top part of the abdominal segments are known as the tergites, while the plates on the underside of the abdomen are known as sternites. The six segments applies to females; most males have seven, and the tip of the abdomen is less pointed, usually rounded.
Most female insects have an egg-laying tube, known scientifically as the ovipositor. This can be sharp and sword-like, as in bush crickets, or a long, thin tube, as in Ichneumons (close relatives of the stinging insects). In wasps and bees, and many ants, this tube is modified into a stinging apparatus, connected with a venom gland inside the abdomen! This is usually not seen till the insect uses it; it flicks in and out effectively like a hidden blade. This is also the reason why males cannot sting.
The single curved piece in the front part of the thorax, just behind the head, and extending to the sides of the thorax, is known as the pronotum. The central panel is known as the mesoscutum, while the back part of the thorax is known as the propodeum. These features are useful to take note of; they are important in differentiating species. It must be noted that these features appear (at least to the layman) more distinct in social wasps, and less so in solitary wasps and bees.
The head of most bees and wasps show this structure. The mandibles are the two jaws, which the insect uses for various purposes, but mainly for chewing food, killing prey and gathering or chewing nest building material. The part just above the mandibles is known as the clypeus. The shape of the clypeus can sometimes be a hint for differentiating species in a certain genus. Above the clypeus, there is the frons, which is essentially the insect's forehead. From two small points called antennal sockets the antennae are attached.
Insects generally have two sets of eyes! The two main eyes are the large, distinct ones at each side of the head. These are compound eyes; they see things like a caleidoscope or like many tiny screens forming one image! This is the reason why some insects have such good vision; many have a nearly 360 degree field of view! This is one reason why it is so difficult to swat a fly without it escaping with precision. Bees and wasps also have good vision, as mentioned previously.
There are also three simple eyes, right on the top of the head, known as the ocelli. Their primary purpose is probably to distinguish light intensity and/or colour.