[094] Coreus marginatus, Dock Bug

[094] Coreus marginatus, Dock Bug

Introduction

Coreus marginatus, the Dock Bug, is a medium-sized insect in the order Hemiptera that feeds on plants like docks and sorrels.

I will include an introduction to Hemiptera and Shield Bugs, as this is our first true bug.

Taxonomy

Kingdom – Animals

Phylum – Arthropods

Class – Insects

Order – Hemiptera (True Bugs)

Suborder – Heteroptera (Typical Bugs)

Infraorder – Pentatomomorpha

Superfamily – Coreoidea

Family – Coreidae (Leaf-footed bugs and squash bugs)

Genus – Coreus

Scientific Name – Coreus marginatus

Name

When used informally, the word bug can have a very general meaning to include all insects, arachnids, small crustaceans and molluscs, and even worms. It is also, of course, used for pathogenic bacteria and viruses – and for computer or equipment malfunctions! The word is at least four hundred years old, may be cognate with bud, and originally meant a bedbug or a beetle.

The species has been known for a long time and the genus Coreus was created in 1794, possibly named from the Ancient Greek koris, ‘bedbug.’ There is a sort of visual margin to the abdomen of Coreus marginatus.

Hemiptera

It is almost impossible to keep up with changes in taxonomy because it is changing fast, it’s never agreed by different authorities and it’s very complicated. Wikipedia tries its best but can’t cope with the fact that a change in a high order insect designation can involve changing up to 100 000 separate entries! As I go up and down taxonomic trees, the names sometimes oscillate and numbers of species also vary. I will try to describe how things are but I do not claim to be accurate, consistent or up-to-date!

The order Hemiptera has about 80 000 species, known as Bugs. Like many words in the world of science, the informal word bug has been appropriated by entomologists for a particular meaning so they are almost always known as ‘True Bugs.’ What defines Hemiptera is the structure of the mouthparts but they are named from their wings. ‘Hemi-ptera’ means ‘half-wings,’ and in many species the forewings are hardened near the base and membranous at the end. It’s like half the elytra of beetles and at rest these insects can look like beetles. (See [086] 7-spot Ladybird for an introduction to beetles.)

Hemiptera are hemimetabolous. It is a diverse order including aphids, bedbugs and others but most of the ones we will meet are shieldbugs.

Within Hemiptera is a suborder, Heteroptera, with between 25 000 and 40 000 species. Sometimes this suborder is known as ‘true bugs.’ When Hemiptera are ‘true bugs,’ the suborder Heteroptera can be called ‘typical bugs.’ Hetero-ptera means different wings for exactly the same reason that Hemiptera are called Hemiptera.

Until recently Heteroptera was ranked as an order. (That’s why it ends -ptera.) Its status and name are still subject to discussion.

Shield Bugs

Within Heteroptera, the largest infraorder is Pentatomorpha, and within this infraorder we will consider just two of its superfamilies.

• Pentatomoidea – about 7 000 species of Shield Bugs or Stink Bugs. They have a well-developed hard shield over the thorax (technically, it’s a scutellum,) and they have glands that can produce an unpleasant defensive odour.
• Coreoidea – another 3 000 species, very similar to Pentatomoidea.

You have to accept that within Pentatomorpha, some are called shield bugs, some are called stink bugs, and some are not called either. And, of course, some bugs outside Pentatomorpha may have similar names.

To be honest, all the bugs in Pentatomorpha (and some less closely connected bugs) look like the same kind of organism and if you find one on a plant you will need your identification skills (or help from social media.) We will see a few in forthcoming blogs.

Description

After all that general introduction I can’t say much about Coreus marginatus. It’s light brown in colour and speckled, with long antennae. The shield has a flat, two-tone margin towards the end.

You have to be careful with all shield bugs, which are hemimetabolous. You may see several instars in their development (probably only the latest ones) and be prepared for them to look significantly different. You will need to consider identification charts with large numbers of organisms in a variety of stages.

Habitat

The Dock Bug is found throughout Europe, Asia and Northern Africa. The larval stages and the adult do feed on docks.

Other Notes

I have had to simplify this post to keep up with the taxonomy. I was going to include some other species that have now been moved to maintain taxonomic proximity.

See also

By an accident of alphabetical randomization, the closest relative of this bug is coming tomorrow …