Western conifer seed bug
The western conifer seed bug, Leptoglossus occidentalis is a large brown bug native to North America which has become established in Britain since 2007. It feeds on pines but causes no noticeable damage to garden trees.
Scientific name Leptoglossus occidentalis
Distribution First reported in Britain in 2007, established in England and Wales
Food Sap feeder on pines, Pinus and some other conifers
What is western conifer seed bug?
The western conifer seed bug Leptoglossus occidentalis, is a large reddish-brown squashbug that can reach 2cm (¾in) in length. There is a white zigzag line across the centre of its wings and it has leaf-like expansions on its hind legs. It feeds on the sap of pines and some other conifers, especially on the seed cones. The bug is native to North America and was first reported in Europe (Italy) in the late 1990s, it reached Britain in 2007 and is becoming widespread in England and Wales.
The adult insects can fly and they are attracted at night to bright lights. They also have a tendency to seek shelter in buildings as the weather turns cooler in the autumn. During winter they can become active indoors and are sometimes found on windowsills.
This species is sometimes confused with another species of true bug which may be of more concern, the Brown Marmorated Stink Bug (BMSB). Western conifer seed bug is larger with noticeably flared hind legs. BMSB is not yet known to be established in the UK.
Western conifer seed bug is unlikely to affect the health and vigour of garden trees and so control measures in the home garden are not necessary. If found indoors the bugs can be placed outside.
You can report sightings of this bug in Britain here.
Western conifer seed bug overwinters as adults in sheltered places such as under bark and in buildings.
In spring the adults emerge and females lay up to 80 eggs on the foliage of conifers. After two weeks the eggs hatch and the nymphs feed on needles and tender cones. There are five stages of development (nymphal instars) and they become adults in mid to late summer. Larger nymphs and adults feed almost exclusively on developing seeds and cones.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.