What are green shield bugs?
A shield bug is a type of true bug, named after the shield-like shape of the adults. There are more than 40 species of shield bug in the UK, some of which are common in gardens. All shield bugs feed on plant sap although most cause no damage and are part of the garden ecosystem.
There are two types of green shield bug in the UK. The common green shield bug (Palomena prasina) has a bright green body with tiny brown 'puncture marks', and brown wing tips. It's native to the UK and is common throughout England and Wales, but rare in Scotland. The southern shield bug (Nezara viridula) is native to Africa and arrived to the UK in 2003, where it's found typically in southern England. It's green with no 'puncture marks' and has pale green wing tips, rather than brown. In its native range it's known for being a pest of vegetable crops such as beans and tomatoes, however in the UK it has not been reported to cause any problems.
How do green shield bugs breed?
After mating the female lays sometimes hexagonal clusters of barrel-shaped eggs on the undersides of leaves. These hatch into wingless nymphs in around June, which crawl between plants to feed. The nymphs go through five stages of growth, or instars, eventually becoming adults by autumn.
Green shield bugs can often be seen basking in the sun during late summer before they hibernate. Both species fade to a brown-bronze in autumn, which makes them blend in better to autumn colours. They hibernate in grass tussocks or leaf litter and emerge again in May.
Are green shield bugs a problem in the garden?
Our native green shield bug causes no problems in gardens, and is part of the natural garden ecosystem. In its native range, the southern green shield bug can cause distortion to vegetable crops, including beans and tomatoes. However, in the UK it doesn't build up numbers until late summer, by which time our vegetable plants have finished cropping.
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Are green shield bugs harmful to humans?
Green shield bugs are absolutely harmless and pose no threats at all to humans. Some gardeners fear that shield bugs can bite humans but this is not true. However they can release a substance that smells similar to marzipan, when disturbed or threatened. This is designed to deter predators but, again, poses absolutely no threat to humans or pets.
How to get rid of green shield bugs
Green shield bugs are part of the natural diversity of gardens and should be encouraged. There's no need to get rid of them – indeed we should be creating better habitats for them to breed and hibernate, including checking leaves for eggs before popping them in the compost bin, and ensuring there's plenty of leaf litter and tussocky grass for adults to take shelter in winter.