What Are Shield Bugs?
Shield bugs are a group of true bugs (order Hemiptera, suborder Heteroptera) named for their broad, flat, shield-shaped bodies. They belong primarily to the family Pentatomidae, though several related families (including Acanthosomatidae and Scutelleridae) are also commonly called shield bugs. In North America, they are often known as stink bugs due to the pungent defensive chemicals many species produce.
Identification Features
How to Recognise a Shield Bug
- Body shape: Broad, flat, roughly pentagonal or shield-shaped when viewed from above.
- Scutellum: A large, triangular plate (the scutellum) on the back, between the wing bases. In Pentatomidae, it covers about one-third to one-half of the abdomen; in Scutelleridae (tortoise bugs), it covers nearly the entire abdomen.
- Antennae: Five-segmented (the name Pentatomidae comes from the Greek pente = five, tomos = section, referring to the antennae).
- Mouthparts: Piercing-sucking stylets, typical of Hemiptera — used to feed on plant sap or, in predatory species, prey fluids.
- Wings: The forewings (hemelytra) are partly hardened and partly membranous — a characteristic of all Heteroptera.
- Size: Most UK species are 6–17 mm long.
- Stink glands: Metathoracic scent glands produce defensive chemicals (aldehydes) that smell unpleasant and deter predators.
Common UK Species
| Species | Common Name | Size | Colour/ID Features | Habitat |
|---|---|---|---|---|
| Palomena prasina | Green shield bug | 12–14 mm | Bright green in summer; bronzy-brown before hibernation | Gardens, hedgerows, woodland edges |
| Pentatoma rufipes | Forest bug (red-legged shield bug) | 11–14 mm | Dark brown with orange-red legs and pronotal corners | Deciduous woodland, orchards |
| Halyomorpha halys | Brown marmorated stink bug | 12–17 mm | Mottled brown; white-banded antennae; invasive from Asia | Gardens, buildings; spreading in southern England |
| Acanthosoma haemorrhoidale | Hawthorn shield bug | 13–15 mm | Green with reddish-brown wing tips and scutellum | Hedgerows with hawthorn |
| Troilus luridus | Bronze shield bug | 10–12 mm | Dark bronze-green; a predatory species | Woodland, gardens (feeds on caterpillars) |
| Eurydema oleracea | Brassica bug | 6–7 mm | Striking black and red (or white/orange) pattern | Brassica crops and wild crucifers |
| Piezodorus lituratus | Gorse shield bug | 10–13 mm | Pale green with purple-red stripe along the front edge | Gorse bushes, heathland |
Biology and Life Cycle
Most shield bugs in the UK have a single generation per year (univoltine). They undergo incomplete metamorphosis (hemimetabolism) — the nymphs resemble small, wingless versions of the adults and develop through five nymphal instars before the final moult into the winged adult.
Shield Bug Life Cycle
- Overwintering: Adults hibernate in leaf litter, bark crevices, or buildings from autumn to spring.
- Mating: Adults emerge in spring and mate. Males locate females using vibrational signals transmitted through plant stems.
- Egg-laying: Females lay neat clusters of barrel-shaped eggs on the undersides of leaves. Eggs are often arranged in regular rows.
- Nymphs: First-instar nymphs typically remain clustered around the egg batch. Later instars disperse and feed independently.
- Moulting: Nymphs moult five times, with wing buds developing progressively.
- Adult: The final moult produces the winged adult, which feeds and builds fat reserves before entering hibernation.
Did you know? Some shield bug mothers show remarkable parental care. The parent bug (Elasmucha grisea) — a British species found on birch trees — guards her eggs and young nymphs from predators and parasitoids, physically shielding them with her body. This is one of the few examples of parental care in non-social insects.
The Brown Marmorated Stink Bug: An Invasive Threat
The brown marmorated stink bug (Halyomorpha halys), native to East Asia, has become a major invasive pest in North America and is now establishing itself in Europe, including southern England. It feeds on over 100 crop species (including fruits, vegetables, and ornamentals) and aggregates in huge numbers in buildings during autumn, causing significant nuisance. Its arrival in the UK is being closely monitored by DEFRA and the Royal Horticultural Society.
Shield Bugs in the Garden
Most native shield bugs cause negligible garden damage and are interesting, attractive insects to observe. The green shield bug is one of the most familiar garden visitors. To encourage shield bugs and other wildlife:
- Leave leaf litter undisturbed over winter for hibernating adults.
- Grow a range of native shrubs, especially hawthorn and hazel.
- Avoid broad-spectrum insecticides.
Key Takeaway
Shield bugs are distinctive, broadly shaped true bugs with a characteristic large scutellum and piercing-sucking mouthparts. Britain is home to around 45 species, most of which are harmless plant-feeders that add diversity and interest to gardens and hedgerows. However, the arrival of invasive species like the brown marmorated stink bug underscores the importance of monitoring and early detection.