Finding Dung beetles
There are a few different sampling techniques that you can use to find dung beetles and these are outlined below. Team DUMP uses the visual search, sieving and pitfall traps most often.
This is pretty straight forward. It simply involves finding a pile of dung and breaking it apart to look inside and find the beetles. Also look for tunnels at the soil interface under the dung. These can be large enough to poke in your thumb (Geotrupidae tunnel) or as small as the width of a pencil (Onthophagus similis, Colobopterus erraticus). The beetle can be very carefully dug out with a small trowel. Often the best approach is to feel the direction of the tunnel by poking in a finger, then place a ‘marker’ such as a pea stick in the tunnel and dig from one side as tunnels can easily collapse.
This method can be applied to all dung types and the more you do it, the better you will become at spotting the beetles. Some of the small dark coloured ones, such as Esymus pusillus are easy to miss. The use of disposal gloves is recommended.
Lumps of dung are placed in a sieve and vigorously shaken over a pale coloured tray. The dung beetles will drop through the holes of the sieve into the tray below. After a few moments the beetles will start to move around and be easier to spot. In hot weather though, beware that they can quickly fly away. It is useful to rest the sieve and contents on a second tray whilst looking for beetles in the first as some may continue to fall from the dung.
This method works best on may also be used to sieve other organic matter such as flood debris found around the edges of ponds and streams to look for Liothorax niger and L. plagiatus or mixed straw and dung from animal shelters for Oxyomous sylvestris.
We use a round garden sieve with 1cm holes and a white lab style tray but a cat litter tray work equally as well.
A pitfall fall trap is a container dug into the ground so that the top is level with or just below the ground surface. When used to catch dung beetles, a mesh grid can be placed over the aperture and a lump of fresh dung rested on top. Alternatively, some dung can be wrapped in muslin and hung above the container. Dung beetles will be attracted by the smell, fly in, land nearby, walk towards the dung and drop into the container below.
There is the option of adding a killing fluid such as water with a drop of detergent to break the surface tension to have a lethal trap. Please bear in mind the decomposition time depending on which killing fluid is used and check the trap accordingly. With water and detergent, beetles will start to decompose in 4-7 days depending on temperature. Alternatively, maintain a live trap by adding a little loose soil and a small amount of dung in the base of the container. In this instance the trap would need to be checked very regularly, possibly as much as twice daily as predatory beetles such as rove beetles may eat the smaller species. The latter is certainly recommended if a rare species is active in the area.
A rain shield can be added to prevent the container filling with water. This is simply an upturned plastic or good quality paper plate with three or four supports (disposable meat skewers are quite effective and cheap to buy) that is placed over the pitfall trap. Providing the shield is placed at a reasonable height above the trap (10-15cm), it should not reduce efficiency.
Dung beetles bury themselves to escape predation from birds and we can use this ‘dig down’ mechanism to our advantage. A Winkler extractor is more often used to sample leaf litter invertebrates but works really well with sieved dung samples too. In the Winkler method, sieved samples are placed in small mesh sacks which are suspended inside a funnel shaped outer sack, usually of cotton/canvas material. A collecting bottle is situated at the base of the funnel. The whole contraption is hung from a tree branch or frame so that the base of the collecting bottle is held off the ground. Over time the dung sievings dry out and this further encourages the beetles to bury through the substrate and drop into the bottle below. This can be a slow process and may take 2-3 days to collect all the beetles especially if the ambient air temperature is cool but the majority will fall through within the first 12-18 hours. It is amazing how many beetles can be collected in this way and it is therefore essential to keep an eye on the collecting bottle and empty it if required.
The dung to be sampled can be immersed in water and the beetles will, quite quickly, float to the surface. The dung may also float and require weighting – especially applicable to horse dung. This can be achieved by placing some wire mesh over the dung before adding the water (sort of the reverse action for sieving!). The water should poured against the side of the bucket to avoid fragmenting the dung and reduce water discolouration. Beetles can be scooped out with a tea strainer or fine gauge kitchen sieve.
With this method, you will generally be sampling the endocoprid species i.e. those that live directly in the dung and will usually not find any that burrow beneath the soil.
Although some tropical dung beetles are flightless, most species are very good at flying as this is how they locate and quickly colonise suitable dung. A flight intercept trap can be used to catch beetles on the wing. This is a fine gauge net sheet that is stretched taught between two posts or trees. Trays are placed on the ground below the netting to catch falling beetles after they have hit the netting. A solution is placed in the trays to prevent the beetles flying away again. It is very important to think about the placement of the net sheet to maximise efficiency. This method is more often used in tropical rather than temperate environments.
Some British dung beetles such as Acrossus rufipes and chafers e.g. Melolontha melolontha fly at dusk and are attracted to light. These beetles are regularly reported by moth enthusiasts and moth traps can be used to the dung beetlers advantage. There are a variety of light traps on the market (Watkins and Doncaster), some are quite expensive but you can build your own too.