western conifer seed bug
Leptoglossus occidentalis
Common name: western conifer seed bug
Family: Coreidae

Host plants: conifers & angiosperms

Adult size: 0.65 – 0.8 inch (16-20 mm)

Life Cycle: one generation per year (see Special Notes below)
adult – overwinter
egg – 10 days
nymph – 5 instar stages lasting about 8 weeks


Description: Adults emerge from their overwintering spots in mid-May to early June. A few days later, females start to lay their eggs in small groups on conifer needles and leaf stems of garden plants. Eggs hatch in 10 days.

The young nymphs go through 5 instar stages as they feed on conifer needles and the tender tissue of cone scales. During the latter instar stages, when the nymphs have developed their piercing and sucking mouth parts, they will feed on developing conifer seeds.

The final moult into adults occurs by mid-August. Adults are varying shades of brown and look quite similar to assassin bugs and shield bugs. Their abdomen, which is revealed when they fly, is yellow or orange in colour with five black lines clearly defined and running horizontally across the body.

This is a true bug. They belong to a small group of insects called the leaf-footed bugs. This name comes from the flat, leaf-like expansions on their hind legs.


Special Notes: First identified in its native range of  California, Oregon and Nevada in 1910. Species began to expand its range eastwards and northwards in the 1950s…reaching into Canada in 1985 and the eastern seaboard by 1987.

Discovered in northern Italy in 1999, it then began traveling throughout Europe (France, Spain, Switzerland, Austria, Belgium, Germany, Hungary, Poland, Czech Republic, Slovenia and Croatia). By 2008, it was found in Tokyo, Japan and in 2009, Istanbul, Turkey. It is also making its way through England as well as Mexico…and possibly other tropical regions.

Because of its expanded range, the life cycle of this bug varies. In its native warm, temperate regions there is only one generation per year. This holds true for other regions of similar weather patterns. However, in some parts of Europe there are two generations per year…and in Mexico and other tropical areas, there are three generations per year.

Status: I have listed this bug under “Beneficial” as it has a purpose in Nature’s grand scheme of things. However, it can become a bit of a pest to conifer plantations where it can cause damage to the developing seed cones through feeding on the sap.

They can also be a nuisance for their propensity of over-wintering in our homes, whenever and wherever they can find an opening to squeeze through.

They are perfectly harmless, however, except when they are startled or touched. They will then emit an unpleasant pungent, acrid odour.


Posted on September 12, 2014