Window latch
A window trap is a device used in ecological research to catch flying insects. It is used particularly often to catch beetles , and more rarely for other insect orders.
Construction and functional principle
In its simplest form, a window trap consists of a transparent pane (formerly glass, now usually a transparent plastic) with a collecting device (a bowl or a funnel that leads into a collecting vessel) at the lower end, which is hung in the examined habitat . The insect flies against the pane, which it has not noticed, falls down and is caught below. Window traps are normally used as automatic catchers for a long time, e.g. B. for one or more weeks, exposed in the habitat and collected the catch made during this time. In this case, the collecting device is equipped with a poisonous liquid that kills and preserves the trapped insects.
There are numerous modifications of this simplest version of the window trap. The most widespread today is a version with two discs crossing at right angles over a wide funnel. This has the advantage that its catchability is less dependent on the exposure and the wind direction. Another variant uses fine-meshed gauze fabric instead of the disc, which is less susceptible to wind. A variant with a smaller disc is attached to tree trunks in order to catch both crawling insects and those flying in the trunk area that want to climb into the canopy. Variants with opaque panes were even tested, which gave comparable results for many groups. The reason for this is probably the relatively poor flight performance and maneuverability of many small insects.
A related type of trap that usually gives better results for catching two-winged and hymenoptera , but z. B. is unsuitable for beetles, is the malaise trap .
To increase the catchability for specific groups, a device that acts as a window trap can additionally be equipped with an attractant, often a specific pheromone . According to this principle, attractant traps are z. B. the bark beetle traps widely used in the forest .
operation area
Window traps are primarily used to detect species whose imagines are short-lived or very rare or who live in otherwise inaccessible heights. As automatic catchers, they deliver catches over a longer period of time and thus yield much more material than could be captured by searching directly. An important area of work is the capture of adults of rare beetle species, which live for a long time as larvae (difficult to find and often indeterminable) and only have a short-lived imaginal stage of a few days lifespan, which only lives until there is a mating partner and suitable habitat for the offspring has found. Window traps, exposed at different heights above the ground, can provide information about the flight altitude of the respective species. They often provide valuable information as to whether an anatomically flightable species actually shows flight behavior. Window traps are usually used in conjunction with other methods such as B. Traps or extraction methods are used, as a method in itself almost never provides a complete range of species.
Cons and Limitations
While window traps often provide a large number of species, including a particularly large number of which could hardly or not at all be detected with other methods, with this method it is in principle impossible to say whether a captured individual comes from the examined habitat itself or whether it flown in from outside or has been blown in. The method is therefore primarily used to identify species in large areas or entire landscapes.
The use of window traps, like all automatic catchers, is technically very complex and involves a lot of work. They are therefore used almost exclusively in basic ecological research. Technical problems create winds and storms (which can destroy the traps), rain (which can flood the trapping vessels) and undesirable "bycatch" (mass catches of species that cannot or should not be scientifically evaluated, or the trapping of vertebrates).
Since window traps can, intentionally or unintentionally, catch species that are strictly protected under nature conservation law, their use in Germany must be approved by the Lower Nature Conservation Authority.
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- TRE Southwood (1966): Ecological Methods. London (Chapman & Hall).
- Stewart B. Peck & Anthony E. Davies (1980): Collecting Small Beetles with Large-Area "Window" Traps. The Coleopterists Bulletin Vol. 34, No. 2: 237-239.
- Simon Leather (editor) (2005): Insect sampling in forest ecosystems. (Methods in Ecology). (Blackwell Publishing).
- Björn Okland: A comparison of three methods of trapping saproxylic beetles. European Journal of Entomology 93: 195-209.
- C. Bouget, H. Brustel, A. Brin, T. Noblecourt (2008): Sampling saproxylic beetles with window flight traps: methodological insights. Revue d'Ecologie (suite de La Terre et la Vie), suppl. n ° 10: 21-32