What is Lurking in Your Compost Bin?

By  Wil Heeney

To most people, compost bins are just places to dispose of garden arisings and grass clippings. It can be a delicate art form, and those who have been home composters for a while often have close-guarded secret recipes of how they arrange their layers and when to add what.

However, even avid composters may give little to no thought to the fauna which turns everything on the heap from scraps and waste into lovely compost. Most people know that the humble worm plays a part – an organism Charles Darwin believed to be one of the most important creatures in history – but many do not consider the other parties involved. For me, it’s these other creatures within the compost heap that are the most interesting: the invertebrates, the little things that rule the earth. Hopefully, by the end of this short blog, some of you might be enthused enough to get together some basic equipment to seek out some of these little things yourself. This isn’t a complete guide to what’s in the compost heap, but a selection of the creatures you might easily find.

What is Lurking in Your Compost Bin?

Beetles are my specialist subject, and you find lots of different species carrying out different roles in even the smallest compost heaps. The most common you may find are from two families: Carabidae, the ground beetles, and Staphylinidae, the rove beetles.

Ground beetles are generally robust-looking insects that are mostly shiny black, or various metallic colours, although some have spots, stripes and markings of many colours. They have a large size range (2mm to 30mm) and – as the family name suggests – can be found most frequently on the ground. Ground beetles are predators, feeding on pretty much anything they can get hold of, relative to their size. Some are specialist hunters, for example, Cychrus caraboides, the snail hunter. Some have larger eyes to enable them to hunt fast-moving prey, like the springtail-stalker Notiophilus biguttatus.

C. caraboides

Pterostichus madidus

N. biguttatus

Rove beetles generally have an elongated body with short wing cases that don’t cover most of the abdominal segments. Like the ground beetles, they have a large size range (2mm to 30mm) and are mostly brown or black in colouration. The largest rove beetle in Britain is the imaginatively named Devil’s Coach Horse Ocypus olens, a species that some of you might be familiar with. Rove beetles are also predators, feeding on other invertebrates and their eggs, both as larvae and as adults. There are over 1000 species of rove beetle in Britain, making them the largest family of beetle in Britain and Ireland.

Ocypus olens

Philonthus spinipes

Quedius sp.

Our final group is one that you’ll have to have a very keen eye for, and plenty of patience: a relatively unknown group of species, the pseudoscorpions. These false scorpions are very similar to the scorpions you might be familiar with from nature documentaries, or possibly holidays. However, they have no tail and don’t come anywhere close to the size of their tailed relatives. The biggest pseudoscorpion in Britain comes in at a whopping 4mm and is the extremely rare Dendrochernes cyrneus, a specialist of mature and veteran trees where it lives under the bark. You would be very lucky to find one of these, but it’s always fun to look! There are around 30 species of pseudoscorpion in Britain and Ireland, many of them specialists and only surviving in very niche habitats. Some are frequently found in compost heaps, such as the Compost Chernes species Pselaphochernes scorpioides, although microscopic examination of pseudoscorpions is often required to be confident in the identification.

D. cyrneus

P. scorpioides

Before attempting at looking for some of these organisms, you’ll need a few basic items that you may already have in your shed or garage:

  • A pair of gloves, for obvious reasons – as compost heaps and bins are designed to rot down waste, they can be a bit of a disgusting place to be digging around in with bare hands!
  • A garden sieve to separate out the invertebrates from the organic material with a mesh size of around 1cm – this will allow most of the larger species through.
  • Something to catch the organisms in, such as a tray with high sides or a large sheet.
  • A magnifying glass – although this isn’t a necessity. If you enjoy your search and want to make a hobby of it, you can invest in a higher-quality lens. I have a purpose-designed eye loupe that hangs on a lanyard with a x8 and x15. If it’s a sunny day, make sure not to use any lens in direct sunlight as you may accidentally concentrate the sun’s rays and burn the creatures you’re looking at.

If you don’t have a sieve – and I have been known to forget to take mine with me from time to time – you can spread handfuls of compost in a tray or on a sheet.

For me, the next step is identifying and recording what species are in the heap, but that is something I won’t go into here. For more information about identifying and recording any species in your garden or the wider countryside and how this information informs, directs and improves nature conservation please visit www.brc.ac.uk.

Remember to be gentle with any creatures that you find and return them safely to the compost heap when you have finished.