Many substrates in which invertebrates can be found (e.g. leaf-litter, moss, reed-litter, etc.) are difficult to search thoroughly as their fine filamentous nature, or even large unhandleable nature, obscures most of the small animals from our view. This is especially the case when the very animals we wish to capture are almost too small to see with the naked eye and they keep still for several minutes feigning death as a defence mechanism when they have been disturbed. Fortunately it is possible to take advantage of one their weaknesses in order to make them sort themselves out from the mass of obscuring vegetation and this is to use their very dependence upon a specific humidity level to cause them to migrate through the substrate until they fall into a collecting receptacle. A few examples of this form of apparatus are described below:
- Tullgren Funnels:
The Tullgren funnel, named after its inventor, uses the application of heat to the upper layers of a collected mass of the substrate to slowly dry it out. This drying forces the invertebrates to migrate ever lower into the substrate to maintain their appropriate humidity levels. When they reach the bottom of the collected and drying substrate they fall through into a collecting bottle containing either 70% alcohol or ethylene glycol (car anti-freeze) as a preservative.
The funnel itself can be an extremely expensive, formally manufactured, variety with a dozen individual small pots to contain differing substrates but at over £1,000 very few individuals or small organisations will be able to afford such a device. It is not difficult to construct a version from two large galvanised wash bowls; the lower one contains the substrate (leaf-litter or whatever) and the upper one has a hole cut in the centre into which is fixed a 60 watt light bulb. The lower bowl should have a larger hole cut into its base and a large plastic funnel fitted into the hole. A piece of coarse wire mesh should go over the funnel entrance prior to placing the leaf-litter into the bowl. The upper bowl is placed, upside-down, over the lower bowl and the light switched on. Underneath the funnel spout should be placed a glass or plastic beaker containing some anti-freeze to preserve the catch as it drops into the beaker over the week to a fortnight it takes for the heat from the light-bulb to dry out the collected substrate. The exit spout from the funnel should be shortened to provide a larger exit hole for the specimens to drop through in order to prevent any largish animals from blocking the tube.
This method is non-specific in its collection of species and numbers and very large numbers of animals can be obtained from even medium quantities of substrate. Attempts should be made to come to some agreement with other specialists in your area so that groups with which you as a collector can not identify are passed to them for identification. In this way the animals are not wasted and much information with regard to distribution and biology can be added to the national databanks of knowledge. Indiscriminate loss and wastage of life should be avoided if at all possible - if there is no end result in mind then other methods should be found to extract the animals.
- Winkler Extraction Nets:
Tullgren funnels work extremely well but the application of direct heat from the light-bulb does cause large numbers of mortalities amongst species which can not move very quickly and fail in their attempts to migrate downwards to higher humidity levels. As a consequence a slower method of drying the collected substrate is provided by the Winkler Extractor.
This contraption comprises two net bags, the inner on of which contains the accumulated leaf-litter. The outer bag stands off from the inner approximately 2 inches and is drawn into a funnel shape below the inner bag. The end of this funnel of net is connected to a largish (2lb jam jar sized) bottle containing a preservative (e.g. ethylene glycol). The whole mechanism, once the inner bag has been filled with the collected substrate, is hung in an airy situation, but out of any direct sunlight, such as a garage. The substrate will slowly dry and the invertebrate animals will leave its confines and fall into the net funnel below the inner bag. From this position they will either slide or move down and fall into the jar containing the preservative. The much slower action of this method results in a much greater percentage of the available invertebrates leaving the substrate and being collected for further examination and identification.
- Owen Emergence Nets: