3.2 Sampling flying insects

This video looks at a local volunteer who monitors moths.

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HERMIONE COCKBURN

Although there are 2,500 species of moth in Britain, in the last century alone, 62 have disappeared from the UK because of habitat loss. Local naturalist and volunteer John Nola is devoted to preserving them. So John, how did you get into this in the first place?

JOHN NOLA

It was a childhood love. I collected moths in my childhood. But collecting is unacceptable, and now we monitor the species that we catch.

HERMIONE COCKBURN

This is the contraption that you do it all with.

JOHN NOLA

Yes, this works on the same principle as a lobster pot, except that you've got a light bulb instead of bait. The moths are attracted to the light, can't find the way out. The trap's full of egg boxes into which they settle themselves.

HERMIONE COCKBURN

Why do you do this? What do you get out of it?

JOHN NOLA

Well, I get a lot of pleasure out of it. But the importance of it is that moths are very good indicators of the health of the environment.

HERMIONE COCKBURN

So if John records a wide variety of moth species here on the reserve, it's a pretty good sign that the plant communities they depend on are in good health.

So what do we do now it's all set up?

JOHN NOLA

We let the trap do its work and come back and see what it achieves tomorrow morning.

HERMIONE COCKBURN

So how do you fancy a pint?

JOHN NOLA

[LAUGHS] I could murder a pint.

[MUSIC PLAYING]

HERMIONE COCKBURN

It's like a lucky dip, really. You don't quite know what you're going to get. Look at this one. That is amazing.

JOHN NOLA

This is the canary-shouldered thorn.

HERMIONE COCKBURN

Oh, that's a lovely one.

JOHN NOLA

This moth is called a mother of pearl. If you sort of move it, you can see the sheen on its wings that gives it its name.

HERMIONE COCKBURN

Oh, yes. It's quite beautiful. Like a shell.

JOHN NOLA

It's a very common moth. Its caterpillar feeds on stinging nettles.

HERMIONE COCKBURN

Ah. Well, I can see why it would be common 'round here then.

[MUSIC PLAYING]

So with an abundance of moths in the trap, it looks like Loch Lomond Nature Reserve is in good shape.

JOHN NOLA

We have another new species here. This is called the oblique carpet.

HERMIONE COCKBURN

[LAUGHS] They've got some great names.

JOHN NOLA

Uh-huh.

HERMIONE COCKBURN

Oh, another [INAUDIBLE].

JOHN NOLA

Another [INAUDIBLE], two common rustic, and another [INAUDIBLE].

[MUSIC PLAYING]

End transcript: Video 6

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Large day-flying insects such as butterflies may be caught in a butterfly net, identified and released, but since each insect needs to be stalked, these nets are not so useful for sampling. The number of insects caught is more dependent on the skill of the surveyor than on the number of insects in a population. However, where the identification of the insect is possible without capture, a transect method can be used, similar to the survey of dragonflies illustrated in the video at the beginning of this section.

Moths can be monitored using a light trap (Figure 14). Traps of the type used in the previous video can be run throughout the night and checked the following day.

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Figure 14 A light trap

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A light trap is constructed from a large container such as a dustbin. The interior is filled with egg boxes to provide shelter for the moths. A Perspex cone with the apex removed is inserted into the top of the dustbin to form a funnel down which the moths will drop. An ultraviolet mercury vapour light bulb surrounded by Perspex vanes sits in the funnel and moths attracted to the light drop down the vanes into the cone and hence into the egg boxes in the dustbin.

Figure 14 A light trap

Light traps are widely used for surveying night-flying insects. Traps that are run every night can provide species lists for a particular area and, more importantly, show changes in species diversity with the seasons and over the long term as annual records are compared.