These little guys are one of my favorite insect groups. My sister caught two of them earlier this month, and I was very excited! They are true bugs (from the order Hemiptera, which means “half-wing”), meaning they have piercing, sucking mouthparts which they keep tucked underneath their bodies when not in use. As Hemipterans, they also have wings which are half-covered by leathery, opaque wing covers. The uncovered parts of their wings, which they use for flight, are visible towards the end of their abdomen. They also have another unique feature which they share with their close relatives, the assassin bugs. Their abdomen (the region right behind their legs) extends out past their wings on both sides.
Ambush bugs are predatory insects. They are very well camouflaged and often blend right into whatever flower or plant they are sitting on. These bugs are very common on goldenrod, and as such most species are greenish-yellow, brown, and/or black. Here is a page with pictures of some common USA species: http://bugguide.net/node/view/4833/bgpage
Ambush bugs have several adaptations which make them excellent predators including big eyes and enlarged, powerful front legs. They use these to catch and hold their prey. In spite of their small size (about a quarter of an inch), ambush bugs are capable of subduing insects much larger than themselves such as bees, flies, and wasps. The bugs wait without moving for an insect to come too close, and then they quickly grab it. Once the bugs have captured their prey, they inject venom into their victims which both paralyzes them and liquefies their insides. The bug then enjoys its meal by sucking up this “insect soup.” (Yum!)
Despite their venom and predatory habits, ambush bugs pose no threat to humans. They are too small for their bite to break the skin and can be handled safely. If you find one, try observing it for a while. You may see it catch an unsuspecting insect meal!
Also, feel free to check out this youtube video to see some of the habits of these amazing creatures: http://www.youtube.com/watch?v=ezDOrId-Tq4