What do true bugs look like?

True bugs belong to the Order Hemiptera, suborder Heteroptera. True bugs include bugs such as plant bugs, stink bugs, water bugs and shield bugs.

Size:

Body:

Highly variable.
Commonly widest at wing attachment (wide shoulders) and oval-like but many other forms exist such as stick-like, spindle-shaped, dome-like, and shield-like.
Head mobile.
Appears hard.

Antennae:

Eyes:

Mouthparts:

For piercing and sucking, do not have visible palps (mouthparts that look like a 'chain of beads').
A slightly curved or straight tube (rostrum) originates from the front of the head.
The tube rests in a groove between the legs so that the tip points to the rear end of the insect.
The tube is hinged at the head so that it points downward or forward when the insect is feeding.

Wings:

One or two pairs, if present.
Forewing has a partially see-through membranous tip with a few visible veins. The remaining portion of the wing is hardened and shield-like.
Hindwing membranous, clear or partially see-through with few veins and cross-veins.
Hindwing usually shorter and wider than the forewing.
At rest, wings are held flat over body, and overlapping at least at the tips - hindwings are folded and hidden.

Limbs:

Six legs.
Shape highly variable depending on their lifestyle - for example digging bugs have spade-like legs while predatory bugs may have raptorial legs.

Abdomen tip:

Most habitats on land or in water, including the surface of the ocean out into open sea.
On plant surfaces particularly leaves and stems but some favour roots or flowers.
Amongst leaf litter, on open ground or in soil.
Under bark, rocks or logs.
In or on the surface of freshwater but coming to the surface to breathe.
In the house in areas such as pot plants or cracks in furniture and walls.

They may be solitary or live together in groups.
When disturbed they have a variety of responses. For example they may fly away, run or move out of the line of sight, remain still, drop to ground as if dead, flash warning colours, release noxious chemicals, bite, or swim away and dive.
They are strong fliers with a rapid wing.
Most bugs are herbivores (plant feeders) piercing and sucking nutrients from plants.
Some are active or ambush predators, sucking internal fluids of victims or liquefying tissue of victims for consumption. Their prey is normally eggs, larvae or adults of other invertebrates but some such as the Fish-killer bugs (family Belostomatidae) have been known to eat small fish and tadpoles.
Some such as Bed bugs (family Cimicidae) and some assassin bugs are external parasites sucking the blood of mammals and birds.
Many true bugs are experts at camouflage. They may behave in a particular way or they may use colouration, patterns, and special body forms to help them blend in with their surroundings. For example some look like sticks, leaves, dirt or bark.
In some special circumstances true bugs may also look, smell and behave like other insects. This special ability maybe useful for predation as well as protection.
They are active during the day or night.

Water scorpions and fishkiller bugs (families Nepidae and Belostomatidae) are typically bug like but they have a long siphon tube that extends from their abdomen tip, which acts as a breathing apparatus from below the surface of the water much like a snorkel.
The hardened regions of the forewings of lace bugs (family Tingidae) form a network, much like a lattice fence with the spaces filled with membrane.

Beetles maybe confused with jewel bugs (family Scutelleridae). The scutellum (small triangular plate between wings) of these true bugs is often so enlarged that it covers the wings (eg. cotton harlequin bug Tectocoris diophthalmus). This might be mistaken for the hardened forewings of beetles. Beetles may be distinguished by their munching mouthparts.
Beetles maybe confused with burrowing bugs (family Cydnidae). Beetles and burrowing bugs can be separated by close inspection of the forewings and mouthparts. Beetles have hardened forewings that meet along a midline and mouthparts for chewing or munching, whilst burrowing bugs have sucking tube mouthparts and their forewing has a membranous tip with veins, with the tips of the forewing overlapping at rest.
Praying mantids maybe be confused with some bugs that have raptorial legs for example water scorpions (Family Nepidae), fishkiller bugs (Family Belostomatidae), and some assassin bugs (Family Reduvidae). However unlike mantids they all have conspicuous sucking mouthparts in the form of a beak-like tube.