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Today I saw an image that reminded me of a recent newspaper article that discussed a proposal to introduce ‘foreign’ dung beetles into New Zealand. (I’m assuming it’s a follow-up to an earlier news item from 2009.)

funny pictures-And you think your job  sucks.

Dung beetles do an essential job in many ecosystems, rolling the dung of larger animals into balls & burying it in the soil for their own offspring to feast on as they grow. (While ruminants can digest the cellulose in their vegetable diets, other mammals can’t, & thus a lot of potential nutrients end up in those big ploppy piles of brown stuff.) We have a lot of cows in New Zealand, & thus a lot of cowpats cluttering up our paddocks – & also releasing CO2 and other greenhouse gases into the atmosphere as they slowly decay. Apparently around 5% of our pasture is covered by dung at any one time. You would of course need fairly large beetles to deal with the quantities of manure that our cattle produce – apparently a couple of species accidentally introduced from Australia have become established here but don’t make even a dent in the poo piles, partly because they’re small as dung beetles go & also because they’re not particularly well adapted to eating dung in paddocks.

The idea of introducing dung beetles (from as far afield as South Africa, Australia, Spain & the south of France) as a means of cleaning  up our paddocks isn’t all that new: I remember one of my own uni lecturers waxing lyrical on the subject when I was an undergrad. In that recent news story there was an added impetus to the call for considering their introduction – the idea that in burying all those balls of poo they’d be helping to sequester carbon in the soil, thus doing something towards reducing the carbon footprint of farming. They could also cut nitrous oxide  & methane emissions from the decaying dung & their extensive burrowing would help to aerate the soil – plus burying all that manure could reduce the need for application of fertilisers. Decaying dung is a significant source of those 2 gases – one study found emissions of ’12.8 g m−2 for nitrous oxide, and 1346 g m−2 for methane’ {Hellebrand & Kalk, 2001). (There’s an extended article here on the Science Learning Hub.)

Given that we’ve got a fairly poor record with regard to species introductions (eg rabbits, possums, deer & mustelids – &, from the indigenous species’ perspective, humans as well…), you’d want to be very sure that there wouldn’t be some unexpected downside to bring dung beetles into the country. Not least, through competition with native species. For yes, apparently there are 17 species of native dung beetles in New Zealand. (Another interesting fact that I wasn’t aware of until now. Gosh, I love my job – so many excuses to learn new stuff!) However, they live in native forest, where they are saprophages rather than coprophages, ‘dung beetles’ being something of a misnomer in the case of our native species. Thus they aren’t likely to come into contact with the new immigrants, who will have those piles of bovine excreta all to themselves :)

H.J.Hellebrand & W-D.Kalk (2001) Emission of methane, nitrous oxide, and ammonia from dung windrows. Nutrient Cycling in Agroecosystems 60(1-3):83-87. DOI: 10.1023/A:1012662823291