|Acanthosomatidae - relative sizes|
Shield bugs are the Acanthosomatidae, a family of Hemiptera. There are 55 genera, with about 200 species. It is one of the least varied families of bugs. The number of species is quite low for beetles, and it is not known why this is so. Individually they are fairly common.
Shield bugs, like almost all bugs, live by sucking the sap of plants, usually flowering plants. They have a "layered" defence system. From a distance they are difficult to see because they are camouflaged. Then, they have a tough armoured back. Lastly, if touched, they give off revolting scents, rather like stink bugs (which are a related group).
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Shield bug Facts for Kids. Kiddle Encyclopedia.