I've seen a few of these around and wondered what they were. Susan Reimer explains in the Sun:
[This] variety of stink bug . . . is Halyomorpha halys, which arrived in Southeastern Pennsylvania from Asia in the mid-1990s and has kind of hitchhiked its way into Maryland since.
It is different from the several species of domestic stink bugs that are more uniform in color, less numerous and less of a danger to crops.
This species is distinguished by its patterned legs, antennae and shield-shaped back. . . .
Unlike the domestic stink bug, which is not a threat to crops, this species favors stone fruit trees, such as peach and cherry, and legume crops, such as soybean.
"We have been seeing crop damage in stone fruits in New Jersey and Pennsylvania," said Dr. Michael Raupp, professor of entomology with the University of Maryland. "And we are starting to see it in soybeans."