Hello budding entomologists this blog is about the pitfalls (no pun intended) of invertebrates trapping and surveying. More specifically, I am talking about the phylum Arthropoda and not other phyla, such as Mollusca and Annelida. I am secondly avoiding the subject of Mollusca, as after a weekend of sorting pitfall traps for my dissertation, I would rather avoid discussing this very slimy, pretty disgusting subject!
Within the Arthropod phyla, you are likely to come across all 4 divisions on campus:
- Chelicerate (the spiders-mites usually with 4-5pairs of legs)
- Myriapoda (centipedes-milipedes usually with dozens of legs)
- Crustacea (woodlice in our case, which have biramous, branched limbs a gill and a leg)
- Hexapoda (the six-legged insects, with 3 main areas, head, thorax and abdomen)
There are a number of ways in which one can capture insects for biodiversity assessment work. It should never be a daunting challenge. Although, in saying this, there are a vast numbers of species on campus that are unlikely to have been recorded before. Such species are common and abundant, like Eristalis intricarius see image 1.
The best way to survey for insects is in a systematic pattern and be patient both with the insects and your identification skills. As I have been frequently told, you can only learn so much off others…… the rest is from the dreaded identification books. These will then become easy (yes easy!), as you learn all the specific terms and features.
- To begin, you must start by collecting a few specimens of a range of insects, just to learn your insect classes, orders and then progressing to the superfamilies and families, of the species you are most interested in. An excellent book to do this in the UK (and Western Europe) for class Insecta, is Michael Chinnery’s Insects of Britain and Western Europe.
- Once you have learned the orders and some of the specific families in your preferred subject area, it is time to start thinking about the specific traps you must use to collect your order. The aim is to get the best representative sample of species of the particular group, with the smallest amount of recorder effort. To do this first think about the trap design and the most effective way of catching the type of insect; be it attracted to light, crawls along the ground or is attracted to pheromones etc. A good way is to look at previous papers on the subject, to see if they found any particular items that were excellent attractants and develop them further. In addition the sighting of the trap is also very important, not just to collect the right group but to prevent edge effects from surrounding habitats, disturbance etc so the results are clear. Again, one must know the target group well i.e. their typical habitats/ habits.
- Once you have decided how to trap and where, there are a range of traps you might wish to choose, that are already well-known. To start there is the classic Pitfall trap for crawling insects. This is simply one cup cut off at the top, inserted into another that is still complete of the same make, inserted into the ground. The internal cup is then filled with 50:50 antifreeze to water and can then be removed without disturbing the other, when you collect the sample. For accurate results, the top of the complete cup MUST be flush with the soils surface (i far to often see them proud of the surface!). The top of the trap can also be covered to prevent excess rainfall entering this is just a shallow tray on stilts, so it is about 1cm above the trap. There are then Pan Traps, these are yellow shallow trays filled with water and a few drops of washing up liquid, to break the surface tension. They are aimed at the pollinating flying insects. There is then the simple Butterfly Net, aimed at specific plants or habitats for flying insects and the Sweep Net for those insects actually on the vegetation. There are then various designs of light traps, with different eases of portability, aimed at specifically moths, however, various other specific species groups can be caught using light. There are then the large Malaise traps, these aim to catch-all flying insects, by intercepting their flight path. They then crawl up the material, into a pot full of alcohol, or antifreeze for collection later. Another way to collect insects, is via the Berlese Funnel, effectively using the heat of an incandescent light bulb, to dry out a sample from the litter layer, forcing the invertebrates within to escape desiccation, by going deeper, until they fall into a preservation liquid beneath.
- Before and on collection of the samples, you must have a good system of trap and collection pot labeling in place. This must be firstly for the trap, secondly collecting the samples and thirdly separating the entire contents of a trap into the different orders/families. Finally, the initial labelling must follow each species as it is identified and data entered into a spreadsheet.
- The preservation of your samples is also crucial, as most of the identification can rarely be done in the field. The majority of insects can be put into a 70% ethanol solution however, species with vibrant colours that are large and will not shrivel up on pinning, or those with scales such as moths, should be dried out, relaxed and pinned when time allows. This is because the alcohol can leach colours, and is not suitable for moths and butterflies. Once your samples have been separated into order, possibly family level, it is time to start speciating the samples. For this, you may need a high-powered microscope, forceps, needles for moving specimens, magnifying glasses and many identification keys and guides. Always start with the simple, large specimens first, otherwise you will feel out of your depth almost immediately, which is no way to create a passion for insects, just a major put off! Once each specimen has been speciated, each should be labelled with the date, GPS location, surveyor name, species name, trapping method. This labelling is done for all samples, be they pinned, in alcohol or for excel spread sheet data entry and analysis.
- The species must then all be stored. Those pinned should be placed in airtight containers with a small amount of insecticide, to prevent samples being lost to the species of decay and those preserved in alcohol must not be allowed to dry out.
- However key to any country’s biodiversity, is making sure your records enter local and national systems, so that species trends, distributions and relative importance can be determined, so that habitats and the wider countryside can be protected effectively. Also where necessary, your samples may also need to be verified by the county recorder for the insect group, for near 100% accuracy on the species identifications.