From the UNH Cooperative Extension:
The brown marmorated stink bug (BMSB), Halyomorpha halya, has begun to show up in New Hampshire. This is significant because BMSB (so named because the insect emits a strong, unpleasant odor when crushed) has the potential to be a household nuisance (like multicolored ladybug, but bigger) and a serious agricultural pest.
Native to Asia, this insect showed up stateside in Pennsylvania in 1998. It was first identified in Portsmouth in 2010, and while it is still mostly confined to southeastern NH, there have been a number of confirmed sightings around Cheshire County.
Adult BMSB are brown, about 2/3 inch (16 mm) long and 1/3 inch (9 mm) wide. They have banded antennae (alternating dark and light bands). The rear edges of the body have a white and dark pattern (thus “marmorated”).
It’s important to note that there are some 36 species of stinkbugs in New Hampshire, and most of them are completely harmless. Many of them, like the western conifer seed bug, find their way into houses to pass the winter and cause no problems. Many others are important predators that keep harmful garden pests at bay. If you see an insect that resembles BMSB, make sure you have a positive ID before you reach for an insecticide.
If you suspect you’ve seen BMSB, call UNH Cooperative Eextension to help you with identification, and to help us keep tabs on this pest.
You can find more information on identification and management at http://extension.unh.edu/agric/agpmp/Brownmarmoratedstinkbug.htm
Contact: Dr. Alan Eaton, UNH Cooperative Extension Specialist, (603) 862-1734 or firstname.lastname@example.org