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Science & NatureWhat is That?What is that ... decomposer?

What is that … decomposer?


Recently, as we were composting some kitchen refuse, we were reminded of the critical role played by decomposers in recycling dead organic matter.  Usually out of sight, decomposers include bacteria, fungi, molluscs, and arthropods that return nutrients to the soil.  Earthworms may be the most important and productive decomposing arthropods at the cottage but they are aided by millipedes and others.  Shortly after these perhaps unexpected thoughts, we read an article in the Ottawa Citizen about a millipede recently discovered in Australia.  The new millipede is the first one known to scientists as having 1000 legs.  Who knew most millipedes did not have 1000 feet.  After all, ‘milli’ is Latin for 1000.  ‘Pede’ is Latin for foot.  It seems scientists used the prefix ‘milli’ to express a sense of many, many, many … legs. The article prompted us to think about the millipedes we see at the cottage; to wonder how many feet or legs they have; and, to reflect on the good work they and their fellow decomposers do.

We know we have at least three species of millipede at Three Mile Bay: the American giant millipede; and, two species of flat-backed millipede which have to be distinguished by their scientific names because they have not been assigned distinctive common names.  All of  ‘our’ millipedes have far fewer than 1000 legs.

First of all, it has to be said that we have a favourite millipede … the American giant, the largest millipede in North America, measuring in at sometimes more than 10 centimetres in length, longer than many adult humans’ fingers.  Every year, we see American giant millipedes march across our lakeside deck, or cross the road when we are out for a walk.  We delight in seeing them because we know that they are heading off to eat decomposing leaf matter, helping to turn it to soil.  Most American giant millipedes live in the forest, under the detritus of leaf matter, roots, and wood, where it is warm and damp.  As you can see from the following photograph, the American giant millipede is cylindrical in shape, dark red-brown or black with a red line on the sides of each segment. Like all millipedes, they have two pairs of legs on the majority of body segments.

Both of our species of flat-backed millipede are much smaller than the American giant.  Sigmoria trimaculata is common in eastern North America including at White Lake.  It grows to about 4 centimetres in length and has a flatter appearance than its big cousin.  The yellow dots that run the length of its ‘back’ help us distinguish it from our second flat-backed millipede, Pseudopolydesmus canadensis, which lacks these dots, as you can see below.  Both flat-backed millipedes, like their giant cousin, eat dead leaves and roots as they traverse the forest floor, helping the detritus to decompose.

Some care should be taken if tempted to handle millipedes, especially in the case of the flat-backed ones which secrete a caustic toxin that is irritating to our skin but especially so, if rubbed into your eyes.  The American giant’s secretions are not dangerous, but decidedly malodorous.

Another arthropod decomposer that we have observed at the cottage is the pill bug which also likes moist conditions.  Its diet is largely made up of decaying or decomposing plant matter, but the pill bug can sometimes also be a pest as it too eats living plants.  In addition, it eats and breaks down the shed snakeskins which our forests have in abundance.

Our last decomposers, not arthropods but also doing good work for our surroundings, are the slugs of the Lanark forests.  Field slugs are not always a welcome sight to gardeners, because they, both the slugs and the gardeners, like to eat vegetables.  But, arguing in favour of field slugs, they do not just eat lush green plants, but also dine on dead vegetation and animals.  Most amazing, to us, is the good work they do decomposing poop, taking an important first step in the process of turning it to soil.  They recycle organic matter helping to enrich soils and they are important prey for other wildlife.  The photo below shows a field slug working hard on fox scat.

In the event the question is asked in your household as it was once by one of our young great kids, neither millipedes, nor slugs, nor pill bugs are insects, despite the fact that information about millipedes can be found in most of our general insect books.  One book well worth looking at with your mid-elementary school-age children or grand children is Michael Ross’ Millipedeology which includes a number of fun activities.





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