From apoda to myriapoda

(This post is the last of four about the numbers of legs and toes in the animal kingdom. If you missed the first one, on mammals, you might want to look at it because it explains why I have chosen this theme. It was posted on June 29th: )

Invertebrates are thought to have developed limbs completely independently from vertebrates, and the details of their morphology are quite different. So instead of counting fingers and toes, I shall count (mainly) legs, and my examples are in order of increasing leg count.

At the minimist end are creatures like leeches, that have no feet, i.e. they are apodal. This one was from a pond in Maine, and is probably parasitic on turtles.

Leech or flatworm, Heald Pond, July 2013. One inch?

Moving onward and upward, we leap to the grasshopper. Like all true insects, it has six legs, and the last pair are the real powerhouse: look at those quads (or at least that’s what we’d call them in a human):


On the end of each leg, and on some joints,  are two tiny claws to help him hang on. In addition to six legs, they have two pairs of wings, and two antennae, for a grand total of twelve appendages.

Spiders are of course not insects, but arachnids, and they have eight legs:

Orb-weaver Spider

Each leg ends in a  tarsal segment, from which grow three tiny pincers that the orb-weaving spider uses with great precision to create its web. (Hunting spiders have only two claws.)  Spiders also have two more shorter appendages called pedipalps, visible in the photo, which are used for sensing, digging, and sometimes copulating, so in fact they have a total of ten appendages!

Caterpillars are the larvae of butterflies and moths, which are themselves insects, so like the grasshopper they have three pairs of legs at the front emerging from what will become the butterfly’s thorax, but they also have four pairs of prolegs in the middle on their abdomen, and one pair at the back called claspers. These extra ten legs are cylindrical.


They have a set of microscopic hooks on the base. The impressive total is thus 16 legs, giving me an excuse to use the word hexadecapodal.

The winners in the leg count stakes are the myriapods (another great word/world), a group that includes both millipedes and centipedes.  I photographed these in Ecuador. They are millipedes, with two pairs of legs on the majority of segments, and this order, Polydesmida, usually has 20 segments. The “leggiest” millipedes, however, can have up to 192 segments and 750 legs!

Millipedes mating

The internet is a wonderful thing. In an attempt to work out what this group of four poisonous millipedes was up to, I emailed Rick Brusca at the U. of Arizona, who said “I am not a myriapodologist” (best word of the day) and passed me on to Allessandro Minelli at the University of Padova, who in turn passed me on to Sergei Golovatch of the Russian Academy of Sciences. The generosity of this chain of scholars, all strangers to me, produced a detailed reply in perfect English within less than 24 hours.

“Dear friends,
The picture of the milllipede from Ecuador definitely shows a species (gen. sp.) of the HUGE family Chelodesmidae (order Polydesmida, class Diplopoda). The bright blue colouration is unusual, more characteristic of a different, purely Central American family, but the few somatic characters I can trace are chelodesmid ones without any doubt. The distributions of numerous Polydesmida are aggregate, but whether it involves courtship or not, remains unknown (at least to me). I doubt it, being rather inclined to think that aggregations better protect. The aposematic colouration* seems to favour this assumption as well. Like most larger Polydesmida, Chelodesmidae (basically Neotropical and Afrotropical), are also poisonous (cyanide producers) and STINK almond when touched…
I hope this short account helps.
Best regards, Yours cordially Sergei”

(*’aposematic colouration’ warns predators that the animal is toxic. I was not tempted to touch them, so I can’t vouch for the almond stink!)

For a final flourish, how about this chap in a cave in Borneo? I counted 64 legs, but Sandro Minelli has better eyes, and says there are 32, each with its own shadow, and that two are antennae, not legs.

Long-legged centipede, a cave-dweller

Both Sandro Minelli and Sergei Golovatch tell me it is a Thereuonema sp. (family Scutigeridae, order Scutigeromorpha, Class Chilopoda), common in Southeast Asia. It is a large and extremely swift predator, a distant relative of similarly frightful and much better known scolopendras. Thank you both.

For astonishing insect close-ups, including feet, look at these:



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