It’s Got Legs!!

Is it a hundred-legger or a thousand-legger?  It’s “one of those things with all those legs!”.   “Those things” are members of the sub-phylum Myriapoda, “many-legged,” containing over 16,000 species of centipedes, millipedes and others.  They were some of the first animals to leave water and adapt to living on land about 250 million years ago. 

They share a common habitat and many similar characteristics, but centipedes and millipedes have several distinguishing attributes by which we can tell them apart.  In North America, both animals are between 1/2″ to 6″ in length.  Millipedes are black with light markings and have a round, tube-like body.  Centipedes are pale yellow to dark brown with a flat body.  Both have exoskeletons, a hard outer shell providing protection for the soft parts of their inner bodies.  As the animals grow, they shed their exoskeletons and grow a new one.  Millipede shells are made from calcium, a hard and inflexible material.  Centipede shells are made from chitin, a fibrous substance that is hard to penetrate, but is  flexible to allow the animal to bend or flatten.

All species of centipedes and millipedes have many pairs of jointed legs.  Centipedes have one pair of long, slender legs for each body segment, allowing for high-speed movement when chasing prey or escaping danger.  Millipedes have two pairs of short, stubby legs per body segment that are used mainly for pushing when digging burrows.  While still in the egg, millipedes undergo a fusion of every two body segments, resulting in each segment having four legs.  While milli means one-thousand and centi means one-hundred, the greatest number of legs is 750 and 254 respectively.

Centipedes and millipedes do not compete for food but do share the same habitat, under leaf litter, in burrows of loose soil, and cool, damp places.  Millipedes are decomposers, able to chew and tear plants efficiently.  They cannot break down cellulose easily by themselves, but prefer to eat plants already partially consumed by bacteria and fungi.  Centipedes are carnivores and their first segmented pair of feet end in a set of lobster-like claws used for catching and rending prey including silverfish and cockroaches.  The claws are sharp and contain venom ducts for stunning prey.

Myriapoda generally live in dark, humid places because they cannot protect their bodies against water loss.  Many centipedes have light gathering sensors located over the entire body to help them detect brighter areas and stay well hidden, away from predators with better eyesight.  Millipedes may roll up and play dead when threatened, exposing only their hard exoskeleton to predators.  Other millipede species exude a sticky glue-like substance behind them to slow down predators, and still others have the ability to spray an attacker with hydrogen cyanide from ducts located along each body segment.

Centipedes and millipedes both provide vital environmental services.  Centipedes eat a variety of smaller insect prey including earthworms and household spiders.  Millipedes are detritivores, feeding on decomposing vegetation and organic matter.  Sow bugs, pill bugs and millipedes together reduce the amount of leaf litter built up on the forest floor by about five percent each year.  Whenever you have a chance, I urge you to take a closer look at these wondrous garden denizens.