Is it faeces for dinner, dearest, or a mixed platter? Dung beetle diets

In addition to some highly speculative claims about the health risks of exotic dung beetles there have been claims about some possible negative effects of exotic dung beetles on New Zealand ecosystems. These were recently articulated by Jacqueline Beggs in an opinion piece in the New Zealand Herald. The Environment Protection agency (EPA) considered these possible effects. Then, based on the current scientific knowledge and experience with dung beetles, the EPA decided they were unlikely to occur.

One concern is that native dung beetles might battle introduced dung beetles for food and that the exotic dung beetles will win. Jacqueline cites recent research that native dung beetles do occur in native forest remnants near pastures and that they eat cow poo. Well I find it hard to see how this is evidence of risk to native dung beetles from introduced dung beetles. New Zealand dung beetles have existed for eons without cow poo or any other large mammal dung- they aren’t suddenly going to miss it if it gets eaten by exotic dung beetles! In addition, if there is cow poo in forest remnants then the greatest risk to New Zealand flora and fauna is the presence of cows, not exotic dung beetles.

Jacqueline claims, “The diet and habitat of our native dung beetles was unknown at the time.” We can examine the veracity of this claim by examining EPA documentation related to the approval. The EPA report refers to unpublished (at the time) thesis data from research on native dung beetles. Native dung beetles are clearly described as opportunists that use any food source available to them. Food sources specifically identified are “carrion, humus and various faeces ranging from invertebrate (caterpillar, stick insect, weta, snail), reptilian (gecko), bird (kiwi, emu[moa]) and introduced mammalian dung from possums, rats, pigs, humans and livestock that invade native habitat (A. Jones, unpubl. data).” So native dung beetles are versatile feeders and do not rely on cow poo. The data has subsequently been published in Ecological Entomology and was not “supposition” and “unknown at the time” it was merely unpublished. Jacqueline was a supervisor of the work so is likely to have been aware of it at the time.

There is one more aspect that needs addressing. What do we know about the diet and habitat requirements of the exotic dung beetles? Do the exotic dung beetles prefer herbivore poo? There are many diet and habitat studies that have been carried out on dung beetles for example, see references in the EPA documentation & Dormont et al (2004). This aspect was also extensively reviewed when the EPA conducted their risk assessment of the dung beetles proposed for release.

The 11 species of dung beetles approved for release in New Zealand belong to a group of dung beetles that build tunnels below the cow pat and bury the poo. This buried poo in tunnels makes a tasty, safe home for their babies. They don’t roll up the dung and trundle across the ground with it like their “celebrity cousins” the dung rollers. The 11 species of dung beetles all have a strong preference for herbivore dung and open grassland habitat. There is also evidence (Dormont et al 2010) that dung beetles food preference i.e. herbivore dung is hard-wired and therefore unlikely to change. Adult dung beetles can’t chew so they are limited to foods they can suck i.e. big, sloppy herbivore poo! Dung beetle larvae are confined to the soil under poo until they become adults so they are unlikely to eat anything outside the dung tunnels lovingly prepared by their parents.

In conclusion, there has been a lot of work already done on dung beetles. The extensive pre-release work demanded by some scientists at the University of Auckland is an unnecessary indulgence and a waste of time when research and conservation funds are limited. There are worthier and more tangible risks to the New Zealand environment to spend money on. Dung beetles offer considerable benefits for the New Zealand environment and sustainable farming. Let’s hope they are set free very soon.

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