Millipede or Centipede?

The metric system is still confusing to some.

"How can you tell a centipede from a millipede? Although similar in having many legs, centipedes and millipedes are vastly different organisms and only distantly related. They suffer from a dearth of knowledgeable specialists, both now and in the past, and from erroneous information that has been passed on by word of mouth." Centipedes and Millipedes with Emphasis on North America Fauna by Rowland M. Shelley

According to Mr. Shelley, if the animal has one pair or two legs (one on each side) per segment that are clearly visible on the sides of the body, if the last legs extend backwards behind the body, if it runs fast and bites or tries to bite, the animal is a centipede. However, if the animal has two pairs or four legs (two on each side) on most segments that do not extend, or extend very slightly beyond the sides of the body, if the last legs do not extend backwards behind the body, if it moves slowly and does not attempt to bite, the animal is a millipede.

The millipedes in the images belong to the order Polydesmida, which has about 28 families. As noted by Mr. Shelley above, this is an area that could use some research. Many people think of milipedes as having a much more rounded body than those shown in the images, which is why this order aquired the name "flat-back millipedes." Mr. Shelley notes that the species in this order are often highly colorful, with vivid red, orange, blue, and violet pigmentations in spotted or banded patterns.

This order has the most species and is only one with cyanide in defensive secretions. By the way, the two millipedes are not involved in a cyanide-laced struggle to the death...they're mating.