Nothing annoys an entomologist as much as hearing insects called bugs. Only one order of insects deserves this name: the Hemiptera. Hemiptera means half-winged and in true bugs, the front halves of the forward pair of wings are usually sclerotised or hardened. The back halves of the wings are membranous and used for flying. Presumably, this hardening offers some protection if the bug is grabbed by a predator.
The hemiptera are divided into two large suborders based on whether their wings are sclerotised or not: heteroptera and homoptera. Heteroptera have the sclerotised wings while in the homoptera, the forward pair of wings are totally membranous. Some taxonomists are now elevating them to order status, but they do share other common buggy characteristics.
All true bugs have sucking mouthparts, so most are plant feeders. The exceptions are the assassin bugs which use their stylets to pierce other insects and suck out their body juices. All true bugs that have compound eyes and two pairs of wings. Some bugs, like scale insects, have secondarily lost their wings due to life style but still show the beginnings of wing development during nymph stages. All true bugs also have incomplete life cycles. They begin as eggs of course and then become nymphs, which are small, sexless versions of the adult form. They moult six to eight times on average and eventually develop wings and sex organs, without going through a pupation stage.
Aphids, cicadas and scale insects are all homopterans with membranous forewings or no wings at all. Cicadas are primarily known for their singing in the summer months but aphids and scale insects represent some of the worst agricultural pests on the planet. These little plant suckers not only damage plants themselves but they also carry diseases that devastate crops
Besides the assassin bugs, there are many different true bugs in the Heteroptera: water striders, water 'scorpions' and water boatmen; shield and stink bugs; flower, ground and seed bugs; chinch and lace bugs; leaf, plant and capsid bugs and squash bugs. These bugs all have a beak that can be swung down or pushed forward from the body. The wings when at rest overlap and lie flat over the body. Many are agricultural pests.
This is a huge order of insects, with an estimated 50,000 to 80,000 species occurring worldwide. Wherever there is a plant, there is a bug that will suck its juices.
for more information: http://www.ento.csiro.au/education/insects/hemiptera.html