Insect monitoring

As an entomologist, my methodology is based around catching or trapping individuals so that I can either identify them in the field (butterflies & moths etc) or take them home for closer examination under the microscope (flies, wasps and beetles etc). In this article I will go through some of the pros and cons associated with practical insect trapping methods. Some good examples of insect catching methods are:

1. Hand-netting: Probably the easiest and most accessible way to catch insects is still a hand-net. I find that a good ‘butterfly net’ is my most essential piece of field equipment, along with my note book. Sadly a net is often maligned by people who imagine that the carrier is going to kill lots of butterflies. In fact the carrier is far more likely to be after moths, flies or wasps and most entomologists only kill insects when it is necessary to identify them – in quite a lot of cases it is just necessary to catch the insect for closer examination before releasing it.
2. Malaise trap: This is my own personal favourite – perhaps because it yeilds so many specimens and it does all the collecting work for you! See my seperate Malaise trapping article.
3. Yellow Pan traps: In this technique you lay out yellow or white ‘pans’ filled with slightly soapy water. Insects that are attracted to white or yellow flowers are then attracted to the bright pans and drop into the water where they are caught. I haven’t actually used this method before but it is supposed to be very easy to set up and it can bring in many flying insects that are attracted to flowers. It does have the disadvantage that it can’t be left for long periods and it can be interferred with – eg. by rain or thirsty dogs drinking the water! Most people will empty the pans daily – or twice on a hot summer’s day.
4. Pitfall traps: Very easy to set up – just bury some plastic drinking cups in the soil so that their tops are level with the ground. Fill them with a mixture of water and anti-freeze and to top them off you can place a flat tile supported on 2 or 3 rocks to prevent animals investigating the contents. This method is very useful for collecting ground-dwelling invertebrates, such as Isopods, spiders or beetles.
5. Moth Trap: I ran a Heath Protable Moth Trap during the spring & summer in the 10 years between 1988 and 1998. The project was very successful and provided us with yearly moth population data. Unfortunately, since 1999 we I have not had the help of a resident summer warden and so we have had to finish this project.
6. Photography: Digital photographs can provide useful ‘field memos’ and attractive souvenirs of a field trip, but are not always very useful for identification purposes. This is because, although large insects (eg. butterflies, large moths, grasshoppers and dragonflies etc) can be identified by comparing them to pictures, most insects are not identified by comparing them to pictures. Instead they need to be run through dichotomous keys that rely on the comparison of minute features, such as wing venation, bristles and paternation.