The western conifer seed bug belongs to a different family -- the leaf-footed bugs. But they are more common here in Montana, and they also emit a pungent odor when disturbed, so they are often mistaken for true stink bugs.
When the weather turns cool, these three-quarter inch long bugs start showing up at our doors and windows. These are the handsome adults looking for a nice spot to spend the winter in a semidormant state, waiting to emerge into the warmth of spring. (Just like me, but I digress.) How do they know your house is warm? The same way they find their food -- infrared radiation.These bugs eat seeds in the young, developing cones of various conifer tree species. The high metabolism of developing seeds helps raise cone temperatures more than 20 degrees Fahrenheit above the temperature of nearby branches and needles. When you have eight infrared sensors on your abdomon, the hot, young pine cones attract you like moths to a flame. These infrared sensors are also probably pretty good at finding warm air leaking out of your house in the fall.
That's not all. Males also tap their abdomens on the branch or cone they are perched on, in distinct frequencies and patterns, to communicate in what's called a "substrate-borne vibratory signal." The business end of the abdomen is also where the stinky stuff is stored. It is reported to be a 152:103:8:1.5:1 ratio of hexyl acetate, hexanal, hexanol, heptyl acetate, and octyl acetate (a clear demonstration of somebody, somewhere putting their chemistry degrees to use in unexpected ways.)
Western conifer seed bugs were first identified in California in 1910. They slowly expanded their range across the continent and reached the east coast by the mid-1980's. In 1999, the species arrived in Italy, hitch-hiking in a timber shipment, and they are currently expanding northward into warm houses across Europe.
When they show up indoors, these harmless bugs do not eat or reproduce. But they can still raise a stink if disturbed. They sometimes appear in your kitchen unexpectedly in the middle of winter (again, just like me), roused from slumber by a dose of warmth. When this happens, you can safely evict them by using a tissue or by gently holding them by the antennae. Just don't squash them or grab them bare-handed, or you'll learn why they are easily mistaken for stink bugs.
Behind the lens: Stinky bug photographed with a Panasonic Lumix DMC-FZ20 "point and shoot" on macro mode.