Shield bugs are a group of insects that are named after their hard back covering called a scutellum. This scutellum looks very similar to a shield, and so the common group name emerged. These insects can be found in many backyards, and can be found in many different colours and sizes.
Insects are the most diverse and successful class of animals in the world. They are found among the Arthropods, and so are segmented with an exoskeleton. Every insect has three body segments--the head, thorax and abdomen--and six true legs connected to the thorax as an adult. Most also have two sets of wings, which includes the shield bugs. Of the 29 orders of insects, shield bugs belong to the order Hemiptera.
This order holds the "true bugs," which includes shield bugs and stink bugs. They are well known for the X shape created by the plate on their back and their wings. The word Hemiptera, or "half wing," refers to the fact that the upper part of their forewing is usually thicker than the lower. These bugs have a scutellum, which is a hard triangular plate over their backs. They have prominent "beak" mouthparts for sucking and piercing. The juveniles in this order look similar to the adults, but have reduced wings. Shield bugs can be found in four families within the Hemiptera order. Each has 5-segmented antennae and are shaped similarly with a distinct shield feature.
Pentatomidae are known as the "true shieldbugs," and the family includes the stink bugs which are well known in many backyards. They can have scent glands located on their thorax which allows them to live up to their name if they feel threatened. This family includes the largest shield bugs with a large scutellum, and have hairs which distinguishes them from other families. The other three families were originally classified as subfamilies of Pentatomidae.
Not all species within this family look like shield bugs, but the larger ones can be best identified by the number of tarsi on their legs. Shield bugs in the family Pentatomidae have three tarsi, while this family only has two tarsi. The members of this family are commonly referred to as Parent Bugs because of the care they take with raising their young.
Known as Burrowing Bugs, Cydnidae burrow underground to feed on the roots of plants. They are usually more rounded in shape than the other families, and are also smaller in size, but the scutellum is still very visible. They have hardened spines, which helps to identify them separately from the "true shield bugs" who have softer hairs.
Scutelleridae are the shield-backed bugs because their scutellum completely covers their wings. They also can have scent glands for protection like Pentatomidae, but are usually much smaller in size.