Hemiptera is an order of insects that contains "true bugs", including cicadas, stink bugs, water striders, leaf hoppers, and aphids. This order is estimated to include 50,000 to 80,000 species. True bugs have two pairs of wings. They are also united by their modified mouth parts and method of feeding. Some eat plants, others are predators and eat smaller arthropods, still others, like bed bugs, are parasites on birds and mammals including humans. The true bugs live in a variety of habitats: underground, in the soil and in water, both fresh and salty. (UC Berkeley BioKeys, Hemiptera...It's a Bug's Life by Jon Martin and Mick Webb)