3.1 Sampling on the soil surface

Insects that move over the ground are sampled with a pitfall trap (Figure 13).

Figure 13 A pitfall trap

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A pitfall trap is a container sunk into the ground that collects insects that fall into it. It has a raised cover to allow in insects but prevent larger animals falling in. Water and detergent or kitchen towel are placed in the base.

Figure 13 A pitfall trap

This trap is made by simply burying a large yoghurt pot or jam jar in the ground so that the rim of the container is flush with the soil surface. Insects running along the ground fall into the container and cannot climb out. The opening of the trap is covered with a flat stone raised off the surface with pebbles, allowing insects to enter the trap but preventing small mammals from falling into it. To trap live insects, the bottom of the container is filled with dry vegetation or a folded kitchen towel, paper tissues or similar, giving the insects somewhere to settle. Pitfall traps are good for collecting ground beetles (family Carabidae) and wolf spiders (family Lycosidae).

If insects are to be collected for later identification, water with a drop of washing-up liquid or ethylene glycol (antifreeze) should be added to the trap. Identification of many insects can only be done with dead specimens and sometimes dissection is needed. Collecting any living organism for identification has to be done responsibly and for good scientific reasons.

Now watch the following video which shows a pitfall trap survey.

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Transcript: Video 5

WOMAN

A good way to take a look at bugs and insects is to set a few simple pitfall traps. A coffee cup sunk into the ground and left overnight will soon have passersby dropping in. My guide is entomologist Dave Boyce.

OK, Dave, let's see what we've got.

DAVE BOYCE

OK. All right, now. Let's just pick a few things out. This is my real passion.

WOMAN

Your thing.

DAVE BOYCE

Yeah. And this is a green tiger beetle.

WOMAN

That's a beauty, isn't it?

DAVE BOYCE

He's a day-hunting predator with these very long legs. It means he can run very fast. He's got very big eyes you can see on the front there. So he's finding things. He sees insects from a distance, and he'll either run them down or even fly. Beetles, you don't think of as being good fliers, but tiger beetles are terrific fliers.

WOMAN

The Billy boy of the heathland.

DAVE BOYCE

Very much so, yeah. Right, well, the green tiger beetle is a beautiful animal and lovely to see. But here is the thing that really gets my pulse racing as a beetle twitcher. This is [INAUDIBLE] ground beetle-- beautiful, green-metallic wing cases and this pinky metallic full body. And this is a very, very rare species.

WOMAN

Why is it that some creatures do have such a hard time of it surviving?

DAVE BOYCE

This is a very, very specialised beast in the habitat it requires. It not only needs lowland heath. It needs particular conditions. It likes very open heath and with lots of patches of bare ground. It's very warmth-loving, and the bare ground creates that very, very dry, very hot environment it requires.

And the work the RSPB's been doing here, in terms of opening up areas of heath for this and for a number of other rare invertebrates and other species, is critical to its survival.

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