Stink Bug Mistaken Identity

As the hot summer days move into cooler autumn weather, insects like stink bugs and Western Conifer seed bugs are moving into sheltered areas to spend the winter. They may move indoors and if disturbed will cause an odor, although only one is a true stink bug.

Leptoglossus occidentalis, the Western Conifer seed bug is from the Coreidae family. They are known as "leaf footed bugs", and there is only one species around the Blackfoot Valley.

They have been called stink bugs; which they are not, according to Montana State University entomologist Laurie Kerzicnik. "People tend to think the Western Conifer seed bug is a stink bug. It stinks, but isn't one," said Kerzicnik.

They are brownish and have a flat area on their hind legs, antennae and a diamond-shaped marking on their back where their wings are tucked in.

These bugs can be found in houses loudly buzzing and can be seen sitting or crawling on sunny buildings and trees.

Although they emit a strong odor when threatened they are not poisonous or toxic to humans or animals. The scent is secreted from special glands on their bodies. Female conifer seed bugs are larger than the males and lay their eggs on tree needles and leaves in late spring.

Conifer seed bugs feed on the male flowers of trees and young cones using their long mouthpiece to drill into the seeds in the cones. Host trees include western pines and Douglas fir.

Sandy Perrin of the Missoula County Extension Plant Clinic said in the stink bug family Pentatomidae there are many different species within the Blackfoot Watershed.

Those include the rough, spined solier, western red-shouldered, conspersus, conspicuous, green, and yellow predaceous. The stink bugs are shield or oval shaped and can be found on buildings, under the bark on firewood and on plants.

Some of the species prey on insects and others feed on plants.

"At first glance, both genders look almost identical," said Perrin. Females tend to be larger than males like with the Conifer seed bug. "Comparing the size of several stink bugs lets you determine which are female and which are male; there is usually a noticeable difference in their sizes when placed side by side," Perrin said. That method is reliable only when comparing mature stink bugs.

Although stink bugs are not poisonous, if they are crushed on bare skin, dermatitis has been reported. The rough and green stink bugs have been known to bite.

Both the conifer seed bug and rough stink bug may overwinter in buildings, wood piles, dead dry trees, or hawk and rodent nests.

Stink bug predators include birds, toads, wasp and fly parasites, predatory bugs, and spiders. Native egg parasites, tachinid flies, birds, spiders and assassin bugs are the predators of the Conifer seed bug.

To control these pests, homeowners can make sure window and doors seals are tight.

"It is not advisable to use an insecticide inside after the insects have gained access to the wall voids or attic areas," said Perrin.

Dusting treatments may kill the bugs, but then carpet beetles will feed on the dead stink bugs and then may attack natural products in the home. Aerosol treatments will kill Conifer and stink bugs as well but after the room is aerated more bugs may continue to come in.

"For this reason use of these materials is not considered a good solution to long-term management of the problem," Perrin said.

The Conifer and stink bugs can be gently caught and relocated outside by hand or with a container. Vacuuming the bugs causes them to release their stink which causes a stinky vacuum. If homeowners find them indoors, they need to remember the bugs are just looking to find a warm place to spend the winter.

For more information contact the Missoula County Extension Office Plant Clinic at 258-4213.