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In Britain Shield Bugs are represented by 4 different families; Acanthosomatidae; Cydnidae, ,Scutelleridae, Pentatomidae and world wide there may be over 5000 species but in the UK the number is limitted to about 45. Their distinctive appearance makes them relatively easy to find and identify. An overview to the families and common names is given in Table 1. The British Squashbugs are similar to the Shieldbugs and are represented by 10 species in the Familiy Coreidae Table 2. The excellent photography illustrating each species is credited to contributors below
How Do I recognise Shieldbugs?
These bugs are flattish oval or shield shaped bugs (hence their common names) ranging from 5 - 35 mm in length. Adult shield bugs are attractive insects, easily characterised by their flatish oval or five-sided shield shape (the pentatomids). Many Shieldbugs demonstrate marked contrast in seasonal body colour polyphenism for example the Southern Green Shieldbug or Nezara viridula
is green in summer and turns brown or reddish when enters diapause in autumn .Shield Bugs are sometimes referred to as "Stink Bugs" because when threatened, some produce a pungent liquid from special glands near their hind legs
When will I see Shieldbugs ?
Table 3 : Shows the associated plant hosts where shieldbugs may be found , ubiquitous Hawthorn , Birch , Gorse and Bramble are all good places to start observing these creatures. Unfortunately only about half the British species have common names and these are listed in the table and some are more obscure to find and observe than others.
What Do They Eat ?
Most shield bugs in the main are phytophagous (feeding on plant sap) although some are carnivorous. Shield bugs (family Pentatomidae) are frequently found in large numbers on crops,some are pests of economically important crops such as coffee and cotton Few gardeners would consider them to be pests, although the noxious liquid they produce can taint the taste of some fruit. Most shield bugs need symbiotic bacteria for the digestion of the sap. They acquire this aid-to-digestion at an early age, their mother smears her eggs with the bacteria so that the young nymphs ingest them as they feed on the egg case. Unlike many insects, shield bugs often show parental care, guarding their young from predators. The Parent Bug (Elasmucha grisea) is so named because the female will actually sit on the eggs until they hatch. This reduces levels of attack from parasitic wasps.Little is known about the predatory Shieldbugs that feed on Lepidoptera (Butterfly) and and larvae of Leaf Beetles (Chrysomelidae). .Such members of the predacious subfamily Amyoteinae and useful pest controllers of other as they feed primarily on caterpillars (Lepidoptera) There are 4 members of that subfamily in Britain, Zicrona caerulea, Picromerus bidens, Troilus luridus and Rhacognathus punctatus
Fig 1: The Hawthorn Shieldbug with large red compond eyes and the Rostrum a plant sucking tube visible The Anatomy of Shieldbugs
Shieldbugs have two pairs of wings, folded flat over the back when not in use and sometimes covered by a triangular plate called the scutellum ("small shield") which gives these insects their common name.
Shieldbugs resemble beetles, however they differ in having sucking mouthparts instead of mandibles . The young shield bugs , called nymphs, pass through several moults, or instars taking on adult characteristics at each stage . This article covers shieldbugs belonging to the families Acanthosomatidae, Cydnidae, Scutelleridae, Thyreocoridae, and Pentatomidae, as well as the similar Squashbugs from the family Coreidae.
As they grow,their colour and paternation changes,and to accommodate a larger body size,they have to molt their outer exoskeleton a number of times before they become adults,with fully formed wings(hidden away behind protective wing covers)
Fig 2: Dorsal Anatomy of Shield Bugs ( Hawthorn Shield) Fig 3 : Vental View Green Shield Anatomy Fig 4: Lateral View Green Shield Anatomy Fig 5: Lateral View Green Shield Anatomy Fig 6: The Anatomy Of The Developing Nymph Anatomical Terms
Antenna These in the shield bug are segmented and vay according to family 5 in the Penatmidae
Central Lobe One part of the head ( 3 parts ) used as an identification character in many species
Clavus The inner part of the wing adjacent to the Scutellum
Coxa The first small connecting segnent of the leg
Connexivum This is a lateral extension of the Abdomen
Corium This is the main area of the toughened forewing base
Cuneus The most distal part of the toughened and clear (opaque) base of forewing.
Dorsal The top, back or upper surface of the insect
Hemelytral Membrane The hemelytron is the forewing made up of the Corium,Clavus and Cuneus the lower wing portion distal (Below or lower) to the harder upper wing structure consists of the transparent membrane structure often visible at a distance.
Instar. This term is used to describe the larval stage between two skin moults in sucession. Each species may have varying numbers of instar stages exhibitting the diferrring forms shown in the matrix.
Legs There are 3 sets Hind, Fore and Mid Legs. Each leg is made up of 5 parts ( Coxa, Trochanter , Femur, Tibia , Tarsus)
Ocelli Primitive eyes distinct from the Compound Eye
Pronotum This is a structure which fronts the Thorax . Many species have pointed extensions such as in the Spiked Shield Bug
Rostrum The long tube that many Phytophagous Shieldbugs use to up sap from plants
Scutellum A triangular or shield like plate in the centre of the thorax located just behind the Pronutum.
Sternites Segments of plates visible on the ventral abdomen
Tarsus The foot portion of the leg used for gripping plants and surfaces
Ventral The underside or belly of the insect
The Life Cycle of Shieldbugs
Shieldbugs lay eggs in clutches usually but not always in multiples of 7, Shieldbugs under go a series of stages or instars, which can both resemble ( Eg Hawthorn Shield ) or be quite different from the adult form. Adults mate back to back . Butterflies and moths undergo 'complete' metamorphosis ie abrupt change from caterpillar to flying adult - the Butterfly . The shield bugs hatch from the egg as small simple forms of the adult and undergo four 'incomplete' metamorphic moults, gradually developing towards the sexually mature adult insect.which can fly.Adults have fully formed wings (hidden away behind protective wing covers).As the bugs grow and develop , colour and paternation alter ,and as the body size changes they have to moult their outer exoskeleton a number of times before becoming adult shieldbugs . These Nymph Stages or Instars will vary from species to species .Adults often overwinter and there colour reverts to a dark pigment approaching winter. In the Cydnidae, Acanthosomatidae and Pentatomidae the adults have five antennal segments and the nymphs only four. The nymphs all go through 5 instars (the period between two moults) to become adult.
Fig 7: Green Shieldbug Exuvium left after an Instar Moult
IMAGE WITH THANKS (C) 2007 STEVE GILL
The Shieldbug Families
Acanthosomatidae
The Hawthorn Shield Bug (Acanthosoma haemorrhoidale) is a good example of what a shield bug is and is readily found on the host plant The Hawthorn Shieldbug emerge in April , where they will lay eggs on leaves in batches of up to 24. Nymphs hatch in a short time and resemble the adult at an early stage
The Birch Shield Bug, To which its name infers it feeds primarily on Birch trees but it will use Hazel and Aspen. It lays eggs slightly later than the Hawthorn Bug , in May.
The Parent Shield Bug (Elasmucha grisea) feeds on Birch. Adults hibernate in leaf litter and similar places emerge in May. Egg laying occurs at the beginning of June, with hatching at the end of June Juveniles assemble in close proximity to the hatching site . The female exhibits brood care of the eggs , guarding them. The young Parent Shieldbugs moult into the second instar in around 10 days and are easy to photograph as they follow the "parent" around. .
The Billberry Shield Bug , E. ferrugata is very rare or possibly extinct it is dependent on Bilberry and Cowberry, often found on heaths , which may be difficult to sweep and for this reason it may well be overlooked , nevertheless this is an Extinct or exceptionally rare species .
Cydnidae
The Dark colour of these bugs give rise to the generic name 'Negro Bugs' The Pied Shieldbug Tritomegas (Sehirus) bicolorfeeds on White Dead Nettle (Lamium album). S. bicolor lays about 40 eggs which the female guards until they hatch in early spring or summer. This species has a row of pegs on the hind wing, rubbing these pegs across a horny ridge on the abdomen produces a sound important in courtship. The majority of the 400 world species are burrowers In Britain only 1 of our 8 species burrows most of our endogenous species feed on the roots of plants and live under stones or logs or in leaf litter.
Scutelleridae
This family have an enlarged mesoscutellum (the plate covering the middle thoracic segment) which extends backwards to cover the abdomen and the wings, they are mostly tropical or subtropical and about 400 species have been named so far and all are phytophagous. There are specimens of the genus Eurygaster in Britain, E. austriaca, E. maura and E. testudinaria. The first two spp are rare as they at there northerly limit. European Tortoise Bug, E. maura, feeds on a range of plants and exhibits feigning death and falling off its food plant if disturbed.
The 2 British species of Odontoscelis are difficult to find as they are subnterrean in soil, or more often beneath the sand as they always occur near the coast either over-wintering near or feeding on plant roots.
Pentatomidae
This Shield Bug Family is the largest making up aproximately half of the British fauna. Most species are phytophagous but some are predacious, Phytophagous species such as Murgantia histrionica, the Harlequin bug are pests, in this case of cabbages and other related plants.
The Sloe Shieldbug Dolycoris baccarum. The name Sloe Bug is something of a misnoma, taken from its local name in Sussex (Butler 1924) but there does not appear to be any particular association with this shrub
Southern Green Sheildbug Nezara viridula, can be a serious pest of a wide range of vegetables, field crops and ornamentals, and especially beans, tomatoes, soybeans and lucerne seed crops elsewhere but in Britain it is a relative newcomer . It feeds mainly on the fruiting parts of the plants. The adult is shield-shaped, about 15 mm long and usually green; overwintering adults are brownish purple. The immature stages are brightly coloured with orange, red, black and green.
The Sedate Shield Bug Troilus luridus lives in both deciduous and coniferous woodlands. This is one of four carnivorous British Species whose feeding behaviour on phytophagous insects in trees may be useful. Initially Eggs first hatch though the young feed on the sap of the plants , second and subsequent Instars are predacious. Its dietary habitat predisposing to beetle larvae means that it is more likely to be found in wooded habits and areas around wood piles of decaying timber where beetles are found and perhaps it might be suggested that they also like beetles are active noturnally. Over-wintering occurs as adults, mainly in moss, or bark crevices. They emerge later in the season than the wholly phytophagous Shield Bugs because they need to wait for their prey to grow and become worth eating first. Eggs are barrel shaped and generally laid in regular patterns around pine needle and small twigs in late May and Early June, Batches of 20 but numerous batches may be by the female who can potentially lay up to 200 eggs. Of the phytophagous species a few such as Murgantia histrionica, the Harlequin bug are pests, in this case of cabbages and other related plants.
Blue Shieldbug Zicrona caerulea is aprox 5 mm. long, shining metallic bug with variations in blue or green . This shieldbug is predatory feeding on leaf-beetle larvae in open habitats, usually heathland or moorland. In particular, larvae of flea-beetles (Altica spp.) have been recorded as prey items. The Blue Shieldbug has been found on lowland mosses, lowland heaths, heather-clad fellsides and rough grassland and scrub.
Spiked Shieldbug . Picromerus bidens This shiled bug is also predatory living on larva of lepidoptera and beetles
Squashbugs (Family Coreidae)
There are 10 species of British Squashbug. These look like the shield bugs but generally are flatter or thinner and yellow brown to grey in colouration.. These species are illustrated in Table 2. and their common names, food plants and habitat notes given in Table 4 These bugs are very dependent on habitat with sparse vegetation cover and grasses with exposed ground
Finding Shieldbugs
Shieldbugs may be more readily found after a windy spell on the lower branches of trees or shrubs under or around the tree, On Breezy hot days along the perimeters of Golf Courses with wooded tree cover may yield specimens down wind. Sheildbugs often favour sunny south slopes and can often be seen basking in the evening or afternoon sun. Often when the first initial finds are made the rest of the colony becomes readily apparent Eggs may be found in clusters under leaves and after hatching Nymphs may remain for a while in close proximity to the parent.
Shieldbugs may be swept from tall grass around shrubs using a sweeping net. Alternatively a beating tray may yield specimens when trees or shrubs are shaken.
The ground dwelling shield bugs and squash bugs who like bare exposed earth are a little more difficult to locate.
Knowledge of the host tree or plant may pay dividends in locating species specific shieldbugs. Shieldbugs are admirably blend in to the host plant, Hawthorn Shields (Acanthosoma haemorrhoidale), resembling Hawthorn , The Spiked Shield Bug (Picromerus bidens), resembling Bramble even adapting to provide subtle green variants. Gorse Shieldbugs (Piezodorus lituratus), resemble the pods of the Gorse plant when in fruit, even the humble Bishops Mitre (Aelia acuminata), in less regal moments takes the appearance of a grain of grass with its long elongated body. A keen eye and concentration are required when visually searching. Gardens are often the best starting points for those new to Shieldbugs and internet groups may assist in both Identifying and Recording the finds. Yahoo Shieldbugs.
The weather and season are also important factors. All British species are in the adult stage from approx August/September through to May/June the exception being the Forest Bug (Pentamoa rufipes), which is usually found between July and November. The winter months do not yield productive species with some ground species well hidden in subterrean shelter. Please remember the best place to leave Shieldbugs is where you find them !!
References
1. Shieldbugs and Squashbugs of The British Isles , Evans , Martin & Edmonson, Roger. ISBN0-99549506-0-7
2.Guide to Shieldbugs of the British Isles Series: FIELD STUDIES COUNCIL OCCASIONAL PUBLICATION 85 Bernard Nau ISBN-10: 1851538984
3. An on-line group on the reporting of Shield Bugs UK Shield Bugs
4. UK Wildlife - Natural History on all classes Insect Page
5. HAWKINS ROGER D. 2003 Shieldbugs of Surrey. Surrey Wildlife Trust
6.Chinery, Michael, Collins guide to Insects of Britain &Western Europe, William Collins Sons & Co. Ltd. [HarperCollinsPublishers] 1986
7. Shaw, H.K.Airy 1945 Habitats of Podops inuncta F. (Hem.,Pentatomidae).Entomologist’s Monthly Magazine 81, p42.
Other Articles By The Author
British Butterflies and Mirror
Hoverflies and Mirror
Lens Cleaning and Mirror
Thanks to the following people who have contributed to the matrix, without which this article would not be complete . The author welcomes any contibution of definitive imaging to add as an ongoing document and thanks the following contributors for efforts and photographic skill Steve Gill, Ashe, Richard Rogers , Stuart Read, Steve Covey, Charles David, Alan Hadley, Dave Monk, UK Shieldbugs,
bravenet.com
IMAGE
WITH THANKS (C) 2007 STEVE GILL
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