Wednesday, December 26, 2007

A Nematode Worm

I am an amateur naturalist trying to learn a little about everything living in my garden.

When I started my blog a year ago, in order that I might avoid "species-count overload" (something that raised some comment and debate at the time) I made the rule that I'd confine my attentions to creatures of a 'sensible size' (a few mm upwards). This remains my broad intention. Since, however, a) rules are made to be broken, and b) Santa has recently been kind enough to deliver me a copy of Life In The Soil (James Nardi, The University of Chicago Press) which contains instructions for making a soil-sampling device known as the Baermann funnel, I can't resist devoting a posting to one of the smaller denizens of my garden.

So, what is a Baermann funnel? As the book says, it is a device whose extreme simplicity belies it's enormous effectiveness in extracting creatures from soil samples. My version is shown in photo 1. To make one, simply cut the end off a plastic fizzy-drinks bottle, fill with an inch of water, stuff a handful of soil inside a muslim bag or stocking (anything with holes small enough to retain the soil but allow small critters to wriggle through), place inside the section of bottle and then stand, cap down, inside a pot so as to position the the lower part of the soil in darkness. Finally stand the whole thing under a source of light (e.g. a desk lamp). Critters in the soil, eager to escape the bright light and heat from the lamp will wriggle down through the soil, through the holes in the stocking and out into the water. After a couple of hours you can unscrew the bottle cap, let the water out into a saucer and look to see who's now swimming around in it....

...and unless you happen to have taken a soil sample from Mars or somesuch, the answer will be: Nematode Worms.

Why? Because, quite simply, nematodes are the most numerous (multicelled) animal on the earth. A square metre of soil may contain a million of them. They are found everywhere (p176 onwards of this book) from the rainforests, to Antarctica, to the mud in the bottom of the ocean, to the soil in my vegetable patch. The much cited quote is from Nathan Cobb, "the father of nematology in the U.S.", who gave the following powerful description of their ubiquity:

"[...] if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites."

Togther with some nice animations pertaining to the body parts of nematodes, The Virtual Nematode site even has a computer-generated movie of the nematode-remains of an earth-blown-apart!

So, what did I find in my Baermann funnel. Answer, within an hour I'd collected more than twenty worms from a single handful of soil. Photo 2 shows one of them (40x magnification, click on photo to enlarge).

Now, those of you who follow my postings will know I generally make some effort to try to establish the specific species of creature I've come across. In the case of my nematode however, I feel I may have met my match. According to the book above some 15,000 species of nematode are known. If this weren't daunting enough however, it's estimated this may represent only about 3% (!) of the number of species awaiting discovering. It's probable that new species are appearing, and sadly that human activity is extinguishing others, all the time. If you want your name associated with the discovery of a new species of animal, you could do worse than to make a Baermann funnel!

I've not tried to work out the species of my nematode. It could be that I am making too much of the difficulty of identifying nematodes however (?). Certainly the UNL Nematology Lab has an online interactive key which looks a good way to get started. It seems you can make some headway by looking to see whether the mouthparts of your worm are those of a herbivore suited to piercing plant roots, those of a bacterivore suited to hoovering-up bacteria, or 'other' (fungivore, fellow nematode predator etc.). If you're an amateur brave enough to be cataloguing the nematode fauna of your back yard do please leave a comment.


the idiot said...

we've just finished the section in Microbiology about infectious human Nematodes. i'm glad to say that the number of Nematodes species capable of infecting humans is drastically less than the projected number of Nematode species.

Roger B. said...

Hello Henry,

I have updated the HTML code for the UK Natural History Bloggers Webring, which you joined about a year ago.

To remain a member of the webring you need to display the code on your site (a bit like the "Brownie Points" section in your sidebar).

To obtain the new code, please email me at


Roger Butterfield

Ashleigh said...

Hi Henry,

I just happened upon your blog - I am very happy to see that you are exploring the creatures in your lawn, and especially happy that you are thinking about nematodes. I am a nematologist, specializing in soil and also marine free-living nematodes (marine sediment is full of nematodes, even more diverse and beautiful than soil nematodes). It's a bit tough to see from your picture but to me, it looks like your picture is an oligochaete and not a nematode. It looks like the animal has chaetae (or setae) which nematodes lack, and the tail is very strange for a soil nematode.

Please keep looking, though, as I guarantee there are nematodes in your soil! One tip on your funnel apparatus: you can simplify it and just have the mesh/fabric/paper towel or whatever is supporting the soil make contact with water - no light needed. This is how I commonly extract nematodes from soil, just suspend the soil on towels on a basket/collander type thing and let it make contact with the water - the nematodes will be attracted to the water and wriggle through the towel into the water in 24-36 hours.

Happy nematode hunting!


Anonymous said...

Thanks for posting this alternate version of Baermann funnel. My son used it for his science experiment.