An illustration of four ambush bugs from Anales de la Sociedad Científica Argentina, found in the Biodiversity Heritage Library. Or parts of ambush bugs.
At the top left is Phymata carioca (the pronotum, the bit that covers the thorax),Phymata incisa (a pronotum and scutellum, or “shield” between the wing joints), Phymata bipunctata, and Phymata husseyi. So now you can tell the difference.
Know your ambush bugs!