I discovered these guys on some yellow flowers in our garden yesterday afternoon. I think the flowers were a type of Rudbeckia, though I admit I’m drawing a blank now, at 9pm, and feel too lazy to go dig up a flashlight and wander out into the garden to check. ;) I can confirm, however, that I also discovered a single individual on a Black-eyed Susan out in our fields the same morning. They’re small – no more than a centimeter / half-inch – and strangely angular. The bright yellow of the lower individual blends in remarkably well with the flower.
These are ambush bugs, a type of assassin bug belonging to the subfamily Phymatinae. I think these are Jagged Ambush Bugs, genus Phymata, for which there are four species listed on BugGuide.net. Although the images for P. fasciata seemed to match these individuals more closely, the only BugGuide records for that species were from the southeastern US. So it may actually be P. americana, which appears to be a northeastern species.
Ambush bugs are predatory. They wait on plants, commonly on flowers, for another insect to stroll by. Flowers make good ambush spots because they’re frequently visited by pollinators. When the unsuspecting insect gets too close, the ambush bug leaps forward to snatch it using its mantis-like hooked forearms (which you can see quite well on the lower individual here). They’re capable of taking prey larger than themselves; like other assassin bugs, they rapidly move to stab captured prey with their sharp ‘beak’ and inject it with a mixture that paralyzes it and dissolves its insides so the predator can then use their straw-like beak to ingest the liquified tissue.
It looks like this is a mating pair, but this BugGuide photo had a comment on it suggesting that the upper individual, the male, is actually just hitching a ride on the lower individual, the female, because she’s larger and stronger and capable of taking down bigger prey than he himself is.