How do you collect them?
There are many ways to catch invertebrates. Given the wide range of invertebrate types no one method is perfect and different techniques must be used in order to obtain the best picture of the invertebrate fauna as possible. The most common methods on Svalbard are:-
2) Pitfall trap
3) Water trap
4) Sticky trap
5) Malaise trap
7) Soil extractions
For flying insects a net is often the easiest method. In areas such as Svalbard it is useful to have a net readily available in order to catch unexpected insects but trapping (see Malaise traps) is often more effective.
* Pitfall trap
For groups active on the surface pitfall traps are often surprising effective. Plastic cups buried with the lip flat with the soil surface and filled with water with a small amount of detergent added. Animals such as spiders and springtails running around will accidently fall into such cups and be trapped.
* Water Traps
Water traps are similar to pitfall traps but consist of a water filled tray placed on the surface. The water film is attractive to flying insects which will often get stuck in the water.
* Sticky trap
Sticky traps are commercial traps used to trap pest species in greenhouses. They consist of a plastic sheet covered by a sticky substance. Most sticky traps are either yellow or blue, the colours attract different insect species and are chosen by the farmer in order to catch a particular pest species.
* Malaise trap
These traps were originally invented by a Swedish entomologist interested in sampling warble flies which parasitise reindeer. They are passive interception traps and work on the simple principle that on encountering an obstacle most insects try and go over rather than around. The trap is a tent-like structure with a central net pegged close to the ground and a sloping roof leading up to the collecting bottle. Insects hitting the vertical net move up the net to the roof. Continuing upwards along the roof they eventually find their way into the collecting bottle.
Pooters are the entomologists stock tool. The basic concept is that the invertebrates are sucked into the collecting vessel. Three types are commonly available depending on from what substrate the invertebrates are to be collected; either mouth operated, electric or by squeezy bulb. Most are mouth operated. The advantage of mouth operation is simplicity and fine control of the amount of suction. However, collecting from substrates such as birds nests with mouth pooters is obviously unadvisable due to unpleasant fine material being drawn through the gauze into the entomologists mouth. All entomologists are familiar with ?pooters-mouth?, a dry mouth caused by the accumulated dust in the mouth following a long successful day pooting. There is also a record of an unfortunate entomologist experiencing the hatching of eggs of Collembola and
beetles in his nose after sucking these up by accident. For unhealthy substrates, a venturi or electrically powered system is preferable, either commercial or home built.
Many species of invertebrate inhabit the soil. Since the majority are small, under 1mm in length, it is necessary to remove them from the soil in order to observe them. Several methods exist. The most common is the use of Tullgren funnels or the improved design of MacFadyen. Although these systems are almost always referred to as extractors it is important to appreciate that they actual expel rather than extract. The animals must be alive in order to leave the soil sample.
In the original funnel as described by Tullgren a mesh is fitted inside a funnel on to which the soil sample is placed The soil sample is always positioned up-side-down in the funnel. A collecting vial is positioned under the funnel and a light bulb over the funnel. The heat of the light bulb progressively dries out the soil. The soil animals start to move downwards away from the dry and warm soil (using the same tunnels that they used to get into the soil, hence the reason why the soil is placed up-side-down in the funnel). Eventually, when the soil is completely dried out the animals drop out of the soil and into the collecting vial. The whole process usually takes around 24 hours depending on the size of the soil sample, the power of the light bulb and how wet the soil was to begin with.
This technique is fast but also fails to remove all the animals since many cannot move fast enough and die within the soil. MacFadyen therefore suggested an improved design. Here the soil is heated gradually over several days with the temperature applied controlled by a thermostat. With this system the soil is dried over several days, the temperature being progressively increased as the soil dries. In addition a cooling system is employed to ensure that that the lower side of the soil core is maintained at a low temperature further encouraging the soil animals downwards. Often, the cooling system is switch off for the last period ensuring that the soil core is baked dry.
While these techniques are efficient for animals such as mites and Collembola they are less suitable for animals that require a moisture film in which to move, for example the nematodes. Here the O'Conner funnel, a modification of the Tullgren funnel, is often used. The apparatus is effectively a Tullgren funnel but with a tap on the bottom. The tap is closed, soil is positioned in the funnel and water added until the soil is almost, but not entirely, covered. The light is then switched on and the water warmed. The worms then "swim" out of the sample after a few hours and are collected in the water just above the tap. Judicious opening of the tap allows just water with the worms to be removed into a collecting vial.