Bug or Beetle? The Red-legged Shieldbug

Young entomologist Noah Davis shares his discovery of a Red-legged shieldbug (Pentatoma rufipes) he found after it had a narrow escape from a spider’s web.

Whilst out on a trip to Norfolk on Tuesday 17^th August, I spontaneously decided to examine the fenceposts on a porch to see what the spiders had caught. It was mainly different species of fly. It was a very rainy day, so I also checked on the bench below a few of the webs in case some had fallen off of the extremely elastic and strong webbing. Some of the heavier prey had fallen off, along with a large, brown, beetle-like insect with a vibrant orange triangle on the centre of its back. My companions and I held a debate on what (or who) it was. Some speculated a stinkbug due to the alarming orange area, and others (quite comically) a camera that was recording, until a quick Google search told us it was a Red-legged Shieldbug.

What is a shieldbug?

The Shieldbugs, which are members of the order hemiptera, or true bugs, are moderately sized insects with sucking mouths and the appearance of a heavily-armoured vehicle (on a miniature scale). Due to the fact that they have armoured backs, they are often mistaken for beetles or stinkbugs. The difference between a shieldbug and a stinkbug is that one makes a pong, the other doesn’t. (The terms ‘stinkbug’ and shieldbug are sometimes used interchageably, but some sheildbugs are stinkier than others because they secrete a pungent fluid when handled! – Ed.).

What does a Red-legged Shieldbug look like?

In short, a shield. Its antennae are long and so is the head segment, and it has a proboscis. It also has broad shoulders with forward-facing forelegs. The next two legs are parallel with the abdomen and the last two are near the end of the abdomen. All the legs are reddish-brown (hence its name) and the whole back is a glossy golden brown. At the tip of the abdomen, there is a notoriously bright orange point, mostly to show predators that it is dangerous (even if it isn’t, but don’t tell the birds that!). Its wings (yes, it can fly) are what forms the point at the end of its back. There are brown and pale banded ridges of fronds at the perimeter of its back. The bug is about 11mm (11/25 inches) in length.

Where are they found?

Shieldbugs are distributed all over the British Isles and continental Europe. They are found near trees or forests.

Bug or Beetle?

Noah and his friends initially thought that their shieldbug looked ‘beetle-like’. There are a couple of ways to tell the difference between true bugs (Order: hemiptera) and beetles (Order: coleoptera). Beetles have chewing mouthparts but in bugs the mouthparts are shaped into a tube, called a rostrum, used to suck liquids. This is often tucked underneath the bug. Beetles have forewings which are hardened to provide a protective covering for the delicate hindwings. When you look at a beetle’s back these make an ‘X’ shape. In shield bugs, the forewings are often thinkened at the base. When you look at at their back, the folded wings make a ‘Y’ shape.

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