some most virtually all hopefully all people interested in animals, I have a dark, guilty secret: I covet and collect dead bodies. In fact I’m of the opinion that if you’re interested in animals and are not interested in dead bodies, there’s something wrong with you. How can you not be interested in – nay, fascinated by – anatomy, variation and functional morphology, and how are you going to learn about this if not by looking at, and manipulating, dead bodies and their constituent parts? Few of us have ready access to museum collections, and building up a collection of specimens yourself is easy (assuming, that is, that you have at least some interaction with the natural world).
While dissection and soft-tissue manipulation has its uses, we mostly want to get the corpses we obtain down to their bare bones; preferably in the cleanest, quickest, easiest way possible. In my efforts to do this, I’ve tried most techniques I can think of: burial in soil, burial in compost heaps, arthropods, live yoghurt, chemicals, mechanical maceration, sun-drying, softening in water, boiling, microwaving. Some techniques work, some fail. The area is hindered by the fact that, while there is some good literature on the processes of decomposition (Weigelt 1989, Machel 1996, Carter et al. 2007), there isn’t really anything like a ‘how-to guide’ should you need to carry it out in a controlled manner. Or, if there is, I’m not aware of it. Thanks to two of my closest colleagues I’ve recently been discussing the topic of controlled decomposition quite a lot. Here are my various thoughts and recollections, some of which you might find interesting or useful. If you’re squeamish: err, hell-o-o, why are you here?
Soaking, boiling and microwaving
First of all, let’s look at some lesser-known techniques, and at their effectiveness. On a few occasions I’ve soaked carcasses in water: if enough time goes by, all the soft tissues fall away, and clean bones are the result. However, this can be a very disgusting and pungent technique, you are generally constrained to small dead things, and algae can stain or even ruin the bones entirely. It works best on specimens that have relatively little soft tissue attached. The hedgehog jaws and newt and frog skeletons you see here were all prepared in this manner.
Boiling works well, but only when much of the soft tissue has already been removed. I once used it on a frog corpse and all I ended up with was a hot frog corpse. The major disadvantage is that most of us can only do boiling indoors: I’m not fond of filling my house with the stench of boiling cadavers, nor are most people I know. Stig Walsh once introduced me to the wonders of microwaving. Unsurprisingly, heating corpses to high temperatures causes skin, flesh and other tissues to come cleanly away from bones. I say that this is unsurprising because we use this technique whenever we cook carcasses for consumption. Anyway, Stig and I once microwaved a dead cat and the results were outstanding. On the down side, it took a long time (about an hour) and hence used a lot of power, plus it created a god-awful stink. If it was my microwave, I’m not sure I’d want to use it afterwards to cook food with.
Ants, woodlice and other arthropods: your friends
Arthropods are your friends. Ants are outstanding at defleshing and cleaning the skeletons of small animals, and everyone who’s ever used the internet will know this well thanks to that video where ants deflesh a gecko skeleton. Of course, the constraint here is that you need ready access to a healthy ant colony. I’ve never had that, and so have never used ants. Isopods – woodlice – also work well if things go to plan. An outside colony of several hundred woodlice, discovered living under rotting wood, were used to deflesh a starling corpse. Within a week they’d done a brilliant job, and a relatively clean skeleton was the result. High encouraged, I started a captive colony and got them to work on a partially defleshed (and fully eviscerated) sparrowhawk corpse. However, I’ve learnt that maintaining woodlice colonies indoors is difficult: they dry out quite easily and require high humidity [hamster skeleton below prepared using 'corpse-in-a-box' technique: see below].
Dermestid beetles are also used by some people, and in fact some museums have large desmestid colonies used specifically for defleshing carcasses. Back when I kept pet lizards, I used to keep a dermestid colony, but I never had enough of the insects to use them in carcass processing (they’re relatively expensive) and I reckon you must have a healthy colony of several hundreds for things to work. Furthermore, I found that they chewed on the bones, leaving noticeable damage. The solution to this might be to remove the material as soon as it’s defleshed. I’d be interested to hear from anyone who has experience in using dermestids, as I’ve heard good things.
The corpse-in-a-box technique
Flies (more specifically, their larvae) and burying beetles are also good, and particularly so because they rapidly find a carcass once it’s available (sometimes within minutes, literally). A while ago it occurred to me that – so long as flies and burying beetles can get in and out of a box containing a carcass – then, that should get the dirty work done. So I put a corpse (a slow-worm) in a small plastic tub, broke some small holes in the top, and left it alone for a few months. The results were excellent. The insects got in, ate all the soft tissues, pupated, and left, leaving behind only bare bones and their empty pupal cases. The pupal cases were stuck to the sides of the tub and not to the bones. The bones were disarticulated and slightly discoloured, but that’s all fine.
And on that note, do not go thinking that this method results in an articulated, ready-for-display skeleton: that just doesn’t happen, and I should note at this point that I don’t want my skeletons to be articulated, posed-as-if-standing show-pieces. No, I want disarticulated bones that can be handled individually. This is, of course, because I want the bones for comparative reasons and research. If you do want the bones to be assembled back into a skeleton, you have quite a task on your hands. My friend Trudie and I once assembled the better part of a Common boa skeleton from cleaned, disarticulated bones, and it took months (although we did only a few minutes here and there). If you do keep the bones in their disarticulated state, as I do, it pays to label them (with a fine marker pen) once they’re identified, particularly the vertebrae.
Anyway, the ‘corpse-in-a-box’ technique is now my favourite method. For mammals and birds the technique is pretty messy as, even after all the soft tissue is gone, you’re left with a lot of feathers and/or fur in the box. You therefore have to do a lot of rinsing, carefully discarding and draining away the water containing the dead feathers and/or fur. Because the skeleton becomes disarticulated by this process, various of the bones get entangled in the unwanted material, so you have to gently feel around in the mess, disentangling the bones and taking care not to throw them away. If you are squeamish or don’t like the thought of manipulating dead feathers and/or fur, this is not for you. It is not pretty or pleasant. Some of you will remember the dead mole I obtained in June 2008. Moles actually break down very quickly (I’m not sure why, perhaps because their lifestyle means that their carcasses are covered in a rich assortment of destructive bacteria), and by September 2008, the job was done. As you can see from the adjacent photos, I had to rinse out a lot of dead fur (the black patches on the grass), but the results were worth it.
Once flies and/or beetles have gotten into the box, they need to be protected: if they die, your decomposition project is at an end. So, the box needs to be sheltered from the rain and from extreme heat. I made the mistake of leaving a corpse box exposed to the sky. Heavy rain flooded the box and drowned all the maggots that were happily eating the squirrel corpse inside (you can see all the dead maggots piled up near the wall). The results were pretty grotesque. Soaking in rainwater has softened the tissues: note that bare bone is visible on the squirrel’s hindlimb.
Because the boxes I use for this technique are generally disposable containers like ice-cream boxes, I’m limited to small animals (which is ok, read on). The largest animals I’ve processed in this way have been such things as squirrels, kestrels and polecats (incidentally, all of my corpses come to me as roadkill, or as natural deaths). For larger animals – anything, say, bigger than a squirrel or pigeon – boxes and arthropods won’t work, at least not before the stench of decomposition becomes a problem. Burial is your only sensible option.
Put them under the dirt
In my (dare I say it, extensive) experience, burial is weird in that the remains of carcasses are sometimes completely absent when you try and dig them up months later. Sometimes this is because you lose the exact spot, sometimes it’s because a scavenger got their first (here in Britain this is typically a fox), but sometimes it’s because decomposition has been so rapid, and so thorough, that the whole carcass has been broken down, bones and all. Or, at least, this is what I hypothesise anyway. I’ve lost hedgehogs, rodents, passerines and frogs in the soil, as well as various fish. Of course, all of these animals have relatively small, delicate bones, so their loss isn’t perhaps so surprising. In order to circumvent this problem, I took to burying carcasses in boxes: the carcass was placed in a lidless box, and the whole thing was then filled in with sediment and buried 10-20 cm down. I tried this with two Lesser spotted dogfish (found discarded on the beach at Portsmouth, oh how I love fishermen), thinking that I’d get a few jaw bones out of it at least. But when I exhumed the boxes… nothing.
Anyway, when all goes to plan, burial works well, though it does require a long time (a year or more for a mid-sized animal). The bones may be soil-stained but they’re generally in good shape and in need of only minor degreasing (this involves a day or two of soaking in water with detergent).
Beverley Halstead once wrote of a case where a dead dog was buried in an active compost heap, and had completely rotted down to its skeleton within something like a day (I think this case is discussed by Weigelt (1989), but I can’t be bothered to go check). Inspired, I have on occasion put carcasses into my compost bin, and the results have been encouraging. So far, all I’ve done is throw dead mice and rats into the compost, and then noted over time the speed of decomposition (we compost all biodegradable kitchen waste, as should you). The problem, however, is that – even if the corpse was placed in a box – you’d have to sort the bones out from the substrate, and that sounds like a lot of trouble.
So, there you have it. I’m very happy with the ‘corpse-in-a-box technique’ and would recommend it to others who need to rot carcasses down. I’m interested in hearing other successes and failures as goes controlled decomposition, so please do chip in. There’s one last thing to discuss: unless you have access to lots of land, where do you do your decomposing? My garden is just about big enough for me to hide away boxes and let nature take its course, without anyone noticing. But when larger carcasses have been involved, I’ve had to be inventive. I’ll stop there, but let’s just say that universities rarely keep a close eye on their more unkempt areas…
Refs – -
Carter, D. O., Yellowlees, D. & Tibbett, M. 2007. Cadaver decomposition in terrestrial ecosystems. Naturwissenschaften 94, 12-24.
Machel, H. G. 1996. Roadkill as teaching aids in historical geology and paleontology. Journal of Geoscience Education 44, 270-276.
Weigelt, J. 1989. Recent Vertebrate Carcasses and Their Paleobiological Implications. University of Chicago Press, Chicago.