Millipedes and centipedes – what’s the difference?
The stunning red-shanked douc lives in rainforests in Vietnam and Laos
A colourful pair of millipedes in Borneo
Compared to the other major arthropod groups, myriapods don’t figure highly in the collective imagination. These long, leggy invertebrates, of which centipedes and millipedes are the most familiar, aren’t ubiquitous like insects, or unsettling like arachnids, or delicious like crustaceans. They go quietly about their business in the tight spaces and dark, dank corners of the world: under logs, rocks and bark, and in rotting wood, leaf litter and deep soil. Out of sight, out of mind.
Superficially, centipedes and millipedes look rather alike, with elongated, segmented, armoured bodies fringed with a multitude of jointed legs. The name ‘myriapod’, derived from the ancient Greek for ‘ten thousand feet’, is a spectacular exaggeration. The only millipede (Latin for ‘a thousand feet’) that lives up to its name is a subterranean species from Western Australia that boasts 1,306 legs. Centipedes (‘a hundred feet’) have no more than 200. The European house centipede has just 30 very long ones. A defining difference between the two groups is that centipedes have a single pair of legs per body segment, while millipedes have two. More legs mean more traction, but less manoeuvrability, a trade-off expressed in their respective styles of locomotion. Millipedes are bulldozers; centipedes are rollercoasters.
Millipedes are mostly vegetarian. They have more or less cylindrical bodies and defend themselves by secreting potent toxins such as hydrogen cyanide from glands dotted along their flanks. With lowslung, flattened bodies, most centipedes are nimble predators. Their first pair of walking legs have been re-modelled as piercing fangs that inject venom into their prey.
Millipede mating involves the male transferring sperm from his genital opening to the female’s using specialised legs called gonopods. In centipedes, fertilisation doesn’t involve bodily contact at all. Instead, males deposit bundles of sperm, called spermatophores, on the ground, which are then picked up by females.
But millipedes and centipedes are not the only myriapods. The phylum includes two other groups – pauropods and symphylans – both of which are plentiful in a shovelful of garden soil, but are so easily overlooked that they haven’t even earned common names. At less than 2mm long and with no more than 11 pairs of legs, pauropods look like tiny, compact millipedes. The more centipede-like symphylans are only a little bigger and sport 12 pairs of legs. Males spin silk plinths for their spermatophores. Bizarrely, the females store these in dedicated cheek pouches and fertilise their eggs by licking them as they are laid.
“Millipedes are bulldozers; centipedes are rollercoasters”
At a fishing event in Florida in the early 1900s, a hooked Indo-Pacific sailfish reportedly pulled out 91m of line in three seconds, which equates to a speed of 110kph (68mph). This record has been questioned on the basis of both the reliability of the measurement and the laws of physics. However, more recently, tagged sailfish have been logged accelerating at a rate that, if sustained for just two seconds, would result in a speed of 126kph (78mph). Bluefin tuna, though, can accelerate even faster – over the same two seconds, they could theoretically reach 232kph (144mph).
Bluefin tuna: the ocean’s answer to the cheetah