Western conifer seed bugs (Leptoglossus occidentalis) are true bugs (Hemiptera) in the family Coreidae. It was originally native to the warm-temperate western USA (California, Oregon and Nevada) but has in recent times expanded its range and become an invasive species in parts of Europe.
This species is sometimes coloquially called "the leaf-footed bug", but actually leaf-footed bugs are an entire group of species in Leptoglossus and related genera of the Coreidae; see for example the Florida Leaf-footed Bug, L. phyllopus.
Its hostplants in the native range includes conifers like the Lodgepole Pine (Pinus contorta), the White Spruce (P. glauca), and the Coast and Rocky Mountain Douglas-firs (Pseudotsuga menziesii). Outside the native range it is also found on species like the Eastern White Pine (P. strobus) and Red Pine (P. resinosa) in eastern North America and Europe, and the Mountain Pine (P. mugo), European Black Pine (P. nigra), Scots Pine (P. sylvestris) and Pistachio (Pistacia vera) (pistaches or pistacio trees) in Europe.
The eggs are laid in small groups on the needles or leafstems of its host plants, and hatch in spring. The nymphae go through 5 instar stages before moulting into adults. In the USA the species is univoltine, but in southern Europe it completes two generations a year, and in tropical Mexico even three. In the northern parts of its range, these bugs start to move about widely by September or so to seek crevices for overwintering; they may become a nuisance in areas with extensive conifer woods as they will sometimes enter houses in considerable numbers.
In Europe this species was first reported in 1999 from northern Italy; it had probably been accidentally imported with timber and as it seems more than once, as its presence was subsequently reported from that country almost simultaneously from locations a considerable distance apart. By 2007, it had established itself in the northern Balkans (Slovenia] and Croatia, the Alps (Austria, Switzerland,), and parts of the Czech Republic, France, Germany and Hungary; in 2003 it was found to occur in Spain though this population probably derives from a separate introduction. The 2007 records from Weymouth College (England) and Oostende (Belgium) might also represent one or two further independent introductions. In late 2007, it was found at Wrocław and Miechów (Poland); these animals probably represent a further range expansion out of the Czech Republic.