Bug!

Once people discover that you are a naturalist they will often reveal some of their own interests in the subject. While such interests are usually rather casual in nature, they are invariably sufficient to prompt questions about things that have been seen in their garden or while out walking in the countryside. Just the other day, for example, I was asked to identify a ‘bug’ that someone had found on their arm. A quick glance at the resulting smartphone photograph revealed it to be the final instar nymph of the forest bug Pentatoma rufipes, one of the large, robust and aptly named shieldbugs.

As with other shieldbugs, this particular species goes through a number of moults as it grows. Insects, having a chitinous exoskeleton, have to shed their rigid outer layer if they are to increase in size and this individual would soon moult through into the adult form. The forest bug is one of our largest shieldbug species, the adults may reach 14 mm in length, with a body that is shaped like an elongated heraldic shield that has projecting shoulders (picture an American footballer viewed from the back). The nymph is more rounded in appearance, mottled in shades of grey, green and black, and with patterning which helps it to blend in with the tree bark on which it lives.

Unusually for a shieldbug, the forest bug overwinters as a small nymph, which means that come spring it is already well developed and can quickly gain maturity. The first adults are seen in the last week of June but numbers don’t peak until the first half of August. The forest bug is a common enough species, associated with deciduous woodland and often encountered along the edge of woodland rides. It is thought that the species is mostly vegetarian in its habits, feeding on sap and honeydew, but it will feed on dead insects when the opportunity arises. What I particularly like about this species, and other shieldbugs, is the unusual structure of the forewings. These are part hardened and part flexible, the hardened section when folded over the back forms the ‘shield’ that gives these bugs their name. They are well worth a glance through a magnifying glass if you get the chance.

A baker's dozen

It’s that quiet time of the year, that brief midsummer lull between the sudden rush of spring and the boisterous climax to summer that heralds the arrival of a new generation of birds and insects. Admittedly there are a few young Blackbirds about, naïve and approachable, and the first of the late summer butterflies have been on the wing for a few days. However, a lot of the other more noticeable creatures (like birds and mammals) are quietly going about the business of breeding. This means that it is time to go in search of some of our less obvious insects, including the various bugs that feed on the lush summer vegetation. Some, like most of our grasshoppers and crickets are in their nymphal stages at the moment and look somewhat different from their final adult form. The same is true of the shieldbugs and many other insects. Others have yet to hatch, as evidenced by a cluster of 13 eggs, a baker’s dozen, neatly secreted on the underside of a leaf in the garden at work.

One of my colleagues brought the eggs in to show me, tiny off-white spheres which reminded me of the hundreds and thousands that used to decorate childhood treats. The 13 eggs were arranged so neatly, quite unlike the haphazard approach adopted by some insects. It was not entirely clear as to what sort of invertebrate had laid the eggs; were they the eggs of a moth or something altogether different? In order to find out, I kept the eggs and leaf in a suitable container, checked them daily and waited.

Just yesterday they hatched and I was delighted to see a little host of 13 tiny bugs sitting on top of the now empty egg cases. Over the last few days, a patterned line had appeared on the top of each egg, the shape reminiscent of the silhouette of a red kite in flight. Then the eggs darkened before hatching. I could see that these youngsters were baby shieldbugs, as nymphs they were more rounded in shape than they would be as an adult. Their pinkish-brown bodies strongly suggestive that they were, in fact, young green shieldbugs. The adult green shieldbug is the one that everyone seems to know, often encountered in gardens on ornamental shrubs, raspberries and even runner beans. The youngsters would remain next to the discarded egg cases until their first moult, after which they would attain a smart two-tone green and black livery. Rather than keep them in captivity, we returned them, and their leaf, back to the plant where they had been found. Perhaps we will see some of them again later in the year, or even next spring as adults.

Shieldbugs raise a stink

Many readers will be familiar with the shieldbugs, a group of large and distinctive insects encountered during early summer and autumn. Most shieldbugs can be identified on sight but, with only a handful of the largest and most common species having English names, we know rather less about their distribution and status than we might. Adult shieldbugs will often remain still when approached, only flying off with a loud buzz of wings as a last resort. Such bold behaviour, unusual in an insect, comes from an ability to produce a pungent smell from strategically positioned stink glands.

In shieldbugs, the forewings are hardened in their front half and membranous in their back half. This characteristic feature gives rise to the name Heteroptera (different wings), used to describe these and a number of related insects. The forewings overlap to form a diagonal cross at the front of which a shield-shaped triangle is formed, which gives these bugs their name. A second characteristic feature is the four-jointed beak, known as a rostrum, with which the bugs can ingest fluids (either from plants or other insects). When not in use the beak is folded away underneath the body. Most shieldbugs spend the winter as adults, emerging in spring to mate and lay eggs. Mating is a somewhat protracted affair, with male and female paired end to end for up to three and a half days. The eggs are laid in clusters and, in all but one species, left alone to develop. The barrel-shaped eggs change colour as they mature and as hatching approaches you can see the eyes through the shell. A temporary projection at the back of the head allows the young nymph to push its way out of the shell and into the wider world. In one species, the female sits over her eggs and newly hatched nymphs to protect them from predators. This behaviour has been known about for more than 200 years and gives the species its name ­– parent bug. 

Other shieldbugs with English names tend to be named after the plant species upon which their young feed. Hence the hawthorn shieldbug is most commonly associated with hawthorn, the birch shieldbug with birch and the gorse shieldbug with gorse. Named after its appearance rather than its choice of foodplant, the green shieldbug is probably the most familiar species, though it is not our only green coloured shieldbug. This species can sometimes be found in gardens on ornamental shrubs or runner beans. As a group, shieldbugs are well worth study. Large, approachable and easy to identify, ideally with the help of Roger Hawkins’ Shieldbugs of Surrey (published by Surrey Wildlife Trust), they are well worth the effort.

Looking for wintering bugs

The other morning seemed suitably inviting to get out and about in search of overwintering bugs. Insects can seem a bit thin on the ground during the winter months but, if you know where to look, there are plenty to be found. I made my way to one of my favourite patches, armed with a stout stick, a pooter and a large white net. A pooter is a rather ingenious bit of kit that can best be described as a mini-hoover, with which you can suck up small insects into an observation pot. I started by working my way along the edge of a reedbed, stopping every few feet to position the net low down and to then tap the vegetation above the net with the stick. A fairly firm tap is usually sufficient to dislodge any insects and spiders that have chosen to overwinter in the vegetation. The white of the net enables you to spot those insects that are dislodged as they crawl around amid the bits of plant material that have also been dislodged. Within ten minutes or so I had several dozen individuals crawling around in the net: at least three different species of spider, two species of beetle, a caterpillar and various heteropteran bugs. Many of these were very small – one of the beetles was about the size of a pinhead – and most would need to be examined back at home under the binocular microscope before I would know what they were.


One of the spiders was familiar to me. Its elongated body and the way in which it held its legs – two pairs of legs fully extended forwards of the body and the other two pairs fully extended backwards – made it look like a fragment of grass stem. This was one of the two species of Tibellus spider known from the county. The pale straw colouration of these spiders helps them to perch inconspicuously on dried vegetation and ambush passing insects. Identification of this spider would definitely need a microscope, so subtle are the differences between the two species.


One species that would not need to be taken home for identification was a brownish-green bug, which had dropped into the net as I tapped a gorse bush. This was the aptly named gorse shieldbug, readily identifiable by its appearance and by the forward-pointing spine on its underside. As you might expect, it derives its name from an association with gorse and from the modified wings covering its back that give the appearance of a shield. Overwintering adults are brown in colour but come summer they turn a beautiful yellow-green. It had been a worthwhile visit, with a few more species to add to the list of those recorded from the site.