The quote here is misleading in the extreme, especially if one is interested in accurately recording the numbers of each species of moth in a trap.

A moth trap is essentially a large box with a light on top, cunningly constructed so a moth swooping around the lamp stands a good chance of being guided into the box, and a poor chance of finding the way out again. Inside the body of the trap are placed a number of cardboard egg cartons, on edge, to give trapped moths somewhere to land. Experience (and demented robins) usually forces a net to be put over the whole thing, to prevent insectivorous birds getting in.

Come the morning, it is essential to get to the trap before the contents warm up to any extent; cold moths are torpid, whereas warmer ones are really quite nervous. This varies with species; the Buff Tip moth is both mildly poisonous and extremely well camouflaged, hence is extremely relaxed about being handled. Species like the Large Yellow Underwing moths, by contrast, are very nervous and prone to flying off before the researcher can properly count them; they do so noisily and disturb other moths on the same carton, which is annoying.

Moth numbers vary with the time of year, and species. Cosmopolitan trash species tend to be seasonally extremely common; Heart and Dart moths peak in early June, whereas the Large Yellow Underwings peak in August; both species can number many hundreds in one trap in one night (the larval food-plants are grasses, and these moths aren’t choosy about which species). Rarities are normally those dependent on rare larval food-plants, though some such as the hawk moths can be most spectacular; elephant hawk moths are a lovely purple colour, and approach the size of a small bird.

In ecological terms, moth diversity is a really good clue to how botanically diverse an area is. My own experiments in this field indicate that the portable Leeds trap is probably the easiest tool to use for assessing habitat diversity, though a mains-powered mercury vapour lamp trap does catch more moths.

Finally, macro-moths aren’t all that hard to identify, not if you have a decent guidebook. Pyralidae and micro-moths, by contrast, are quite tricky but tend to be a lot smaller and harder to handle.