PEET - Austral Staphylinidae

Methods | Collecting Methods for Staphylinidae and other Staphylinoidea | Indirect Collection Methods: Carrion Traps

Carrion traps are one type of baited pitfall trap. In general, unbaited pitfall trapping is very popular as a standardized method for collecting surface-active insects. A pitfall trap is a container dug into the soil with the edges flush with the surface. Moving insects encounter the edge of the trap and fall into it. There are a variety of pitfall trap designs and a voluminous literature about the method. Pitfall traps, like all mass-trapping methods, are biased toward highly active insects, particularly predators, and so are particularly effective for collecting many carabid beetles for example, and the more active litter inhabiting staphylinids. However, the method is not well suited for collecting slower moving insects, and/or those species that occur at naturally low densities. It may also be ineffective for collecting many species that tend to cluster around particular microhabitats, such as fungi, dung, carrion, or flowers, including many staphylinoids, but instead might intercept only a few individuals as they traverse the habitat in search of their preferred substrate. Because of these factors inherent in the population and life history characteristics of many species, pitfall trapping (and in fact all mass-trapping techniques) can give incorrect estimates of population size, relative abundance, and the rarity of some species.

To circumvent these problems, we use baited pitfall traps to collect larger numbers of substrate-specific staphylinoids. Many staphylinoids are attracted to decaying substrates such as carrion, dung, and fruits, and actively search for these microhabitats, so a pitfall trap baited with such substrates collects them effectively. Different baits can be more effective in particular regions and habitats. For example, carrion trapping is more effective for attracting many different staphylinoids in some south temperate regions such as New Zealand, where dung is not a major resource because there have never been large indigenous mammals. Likewise in temperate parts of Australia, dung is relatively ineffective for staphylinoids: perhaps marsupial dung is less of a resource than ungulate or carnivore dung. Contrary to these peculiarities, dung is effective bait in the Northern Hemisphere (e.g., Newton et al. 2000), and in tropical forests fruit-baited traps are likely to bring more material than in temperate biomes, because of the greater abundance of fruit as a resource.

After testing many different kinds of carrion bait for staphylinoids, Newton & Peck (1975) concluded that the most effective is squid or octopus, because it maintains a moist state of decay for much longer than other baits (e.g., chicken liver) – sometimes longer than a month, which is generally about the maximum time for which we set traps. This is important because as carrion dries, it generally attracts fewer staphylinoids and more of other things we are less interested in. We buy a supply of bait at the start of a field trip, divide it into small portions (ca. 100 g or 4 oz), wrap those in cheesecloth (which is biodegradable) and store them until use in a freezer or portable cooler if possible.

A detailed description of the carrion trap design that we use, the materials, and operation can be downloaded here. Our carrion traps consist of a few different parts. A 1 quart (0.974 l) plastic container is used as the trap, which is dug into the ground. A large piece of chicken wire mesh is used to attach a box constructed from smaller wire mesh, which contains the bait, and this construction is placed across the top of the trap. The bait is thus suspended above the trap fluid in the container. A piece of polyethylene is also used as a rain cover.

We set the carrion trap in the general area of the flight intercept trap, but far enough away from it (preferably at least 5-10 m and outside the flight path) so the two traps are collecting independently of one another. Once installed, a large boulder or log is placed over the top of the trap to protect it from foraging mammals, some of which are also attracted to the smell of carrion.

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