A thousand legs has a millipede
While a hundred does the centipede
The millipede eats plants
The centipede eats ants
I wonder if any get knock-kneed?
My little limerick about millipedes and centipedes doesn't begin to cover the differences between centipedes and millipedes, but it does point help to point out a key difference between the two (other than the number of legs)- the centipede is a carnivore that primarily eats insects and spiders- while the millipede usually consumes plants or rotting wood and leaves. Oh- and centipedes bite- some even have poison glands. Millipedes on the whole- do not bite- but they aren't defenseless, as you will soon discover.
Another interesting note about these types of millipedes is that they possibly excrete the toxin cynide through their "skin." While handling the above millipede, I did notice a white liquid being expelled from the "skin" of the millipede. Who knew? An interesting abstract regarding this phenomenom is located on the ScienceDirect website. The paper title is Cynogenesis in Plants and Athropods.
source) It, along with the yellow and black millipede shown earlier, are known as "flat back millipedes." Each belong to the Polydesmida family. Members of the Polydesmida family can be identified by the fact that their bodies have 18 to 22 body rings- with 20 body rings being the most common. (source)
This brownish millipede appears to be a member of the Parajulidae family of millipedes. These millipedes look remarkably like earthworms. The one photographed above even flailed around like an earthworm after I caught it. These millipedes are infamous for crawling into houses- typically basements. They have a very unpleasant odor and usually aren't welcome guests.
This semi-lovely black millipede with the red racing stripes is scientifically known as the Narceus americanus. Its common name is the North American Millipede. This millipede is noteworthy in that it is the largest of all the millipedes in North America. It can grow to a length of 10cm- which makes it twice as large as any other millipede in North America. (source)
All of the millipedes pictured here were found in my back yard. There are at least 2 other species that we caught that I haven't been able to get a good photograph of yet. So, why do we need so many millipedes? Consider this quote and decide for yourself:
Throughout Northwest forests, the principal shredder is the cyanide-producing millipede (Harpaphe haydeniana), which has a shining black body and bright orange racing stripes. Since the millipede crushes, filters and then recrushes its dead leaf diet, it increases the availability of nutrients 40,000-fold. After extracting what it needs, the millipede defecates a pellet of partially used nutrients covered with microbial fuel (intestinal mucus). Immediately, a microbial garden grows on the surface and then a soil fungivore comes along and breaks up the pellet, feeds, excretes with its own mucus, and the whole process repeats over and over again until all the nutrients are used up. It is the shredder that is key to the process. The cyanide-producing millipede alone eats 33 to 50 percent of all the dead coniferous and deciduous leaves that come to rest on the forest floor. It is one of the most critical links in the entire soil foodweb. From the article: Small in Size, but Great in Importance by Andrew Moldenke.
Dr. Rowland Shelley wrote an excellent guide to millipedes and centipedes that can be found online at http://www.emporia.edu/ksn/v45n3-march1999/index.html This is part of an great series of online and printed guides that the Kansas School Naturalist produces. The catalog of their articles is at http://www.emporia.edu/ksn/.