biology zoology blog benno meyer worms

Abound with Wormy Things

That is the world we live in

Many things are worm-shaped: spaghetti, shoe laces, leeches, snakes, eels… There must be something about being thin and limbless. The typical worm-like body is, of course, eminently suited to explore and move through narrow crevices and gaps of small dimensions and to roll or coil up to reduce the exposed body surface area in times of danger. But worm does not equal worm and zoologically speaking bookworms, flatworms, ribbonworms, arrowworms, earthworms, roundworms and wireworms have as little in common as cuttlefish have with jellyfish, shellfish have with catfish and silverfish have with starfish.

In spite of the wormy shapes, the different kinds of worm possess very different anatomical organizations and are not at all related to one another. Flatworms, for example, all lack an anus, but ribbonworms not only possess this attribute, they also have an evertable, proboscis-like head appendage termed “rhynchocoel”. Arrowworms are marine, planktonic and highly transparent micro-carnivores with chitin claws around the mouth, whereas earthworms are characterized by a segmented body with tiny bristles, features that roundworms completely lack. Wireworms, the larvae of beetles, are insects of the soil. They, like wormy millipedes, are extraordinarily tough when it comes to tolerating weights on their chitinous bodies (rolled up millipedes of 2 cm length have been reported to survive a weight of just over one pound = approximately 500 g).

Wormy animals, no matter where, are frequently in danger of other wormy creatures: in the water eels and snakes hunt them; on land limbless amphibians, lizards and snakes follow them into their retreats. Some worms, however, get their own back by leading a parasitic existence and eels, snakes and limbless lizards and amphibians make as good a host as any. Propulsion in wormlike animals is more varied than one might expect from their rather uniform body shapes. In roundworms longitudinal muscles on either side of the body flex alternately, causing the animal to slash whip-like from side to side. In earthworms and some wormy caterpillars peristaltic contraction waves run along the entire body from “head to tail”; terrestrial snakes slither sinuously in a horizontal plane or propel themselves by “side-winding” and some of them, of course, are also known to be good climbers. Body undulations in a vertical plane are seen in aquatic leeches, when they swim and also in stretched out marine mammals (the leopard seal is almost snake-like). A coat of tiny cilia allows the flatworms to seemingly “slide” along, whereas wormy slugs operate with a slime trail.

Caterpillars of the family Geometridae and terrestrial leeches have evolved a kind of “looping” as they crawl along, but in terms of locomotory extravagance the Flying Snake Chrysopelea of the Malayan region beats them all: it attempts to glide from tree to tree through the air and sometimes manages – although on most occasions it falls to the ground. That snake inspired me to translate a poem by German 19th century author Wilhelm Busch:

Wenn einer, der mit Mühe kaum, If someone under lots of strain
geklettert ist auf einen Baum, managed to climb a tree up high,
schon meint, dass er ein Vogel wär, and then decides to jump and fly,
so irrt sich der. he will find out he’s neither bird nor plane.

© Dr V.B. Meyer-Rochow and, 2020.
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