These bugs are group of small wide-bodied insects that have raptorial front legs. The front femora are short and as broad as long. The tibiae are tiny and curved. Most are about 3-4 cm. long, but they are able to capture insects as large as bumble bees. They stalk them on flowers, mainly goldenrod, where they are camouflaged by the plant color. Their prey includes wasps, large bees and flies.
Insects in the subfamily Phymatinae are commonly called ambush bugs after their behavior of stalking prey and relying on their camouflage. They have raptorial forelegs with which they area able to capture prey 10 or more times their own size. They belong to a subgroup within the assassin bugs.
Phymatinae are 5.1–12.3 millimetres long. In Phymata, the scutellum is triangular and shorter than the pronotum. In Macrocephalus the scutellum is narrow and rounded and extends to the tip of the abdomen.
These insects usually have a large fore femur and clubbed antennae. The forewing membranes occasionally lack distinct cells The antennae have 4 segments, and there are two ocelli. The beak has 3 segments. The tarsi also have 3 segments. The rear half of the abdomen extends beyond the edges of the wings
Weirauch, C. & James B. Munro (2009). "Molecular phylogeny of the assassin bugs (Hemiptera: Reduviidae), based on mitochondrial and nuclear ribosomal genes". Molecular Phylogenetics and Evolution 53 (1): 287–299.