IN the hinterland of Tamil Nadu a riddle goes thus: Kandaal vandi, thottal chakram (Looks like a train, touch and it’s a wheel).
The answer: millipedes.
If you are one of those who do not mind getting your hands dirty in the soil, these commonly crawling black and yellow creatures ( Anoplodesmus species) would be no stranger. They are millipedes, creatures that are “looked down upon”, though in reality they deserve to be worshipped, a point you might concur with as you finish reading this piece. In some cultures they are revered.
What are they?
Millipedes belong to the class Diplopoda of the subphylum Myriapoda—a group that contains backbone-less animals with “many legs” (hence the term Myriapoda). Myriapoda is a subgroup of the phylum Arthropoda. The term Diplopoda describes them more accurately as they have two (diplo) pairs of legs (poda) in each segment of their body.
The Diplopoda are among the large classes in the animal kingdom, but they live practically in anonymity, eclipsed by their more famous and (more well studied) Arthropod cousins—insects and arachnids. It is a pity that they remain unknown, for, if not anything, they arrived on earth before insects or spiders and have a distinguished evolutionary history spanning nearly 400 million years. There is a theory that the ancestors of insects may actually have evolved from Myriapods. In the field of evolution, everything is subject to doubt and cross-examination, and hence the jury is still out on whether Myriapods or crustaceans are the ancestors of insects.
There are about 80,000 millipede species in the world. Only 12,000 or so of these have been described so far. India is home to over 270 species. In India, millipedes of the order Polydesmida are the most diverse (86 species belonging to 41 genera). More than 70 per cent of Indian millipedes are endemic, many of them to south India where millipedes have been studied better than in other parts of the country. Although the word millipede is derived from Latin words mille (thousand) and ped (foot), the number of legs ranges from 11 to 375.
The North American Illacme plenipes, with a record 750 legs, was recently dethroned as the species with the most number of legs. A team of researchers led by Dr Paul Merk found a millipede, Eumillipes persephone, with 1,306 legs at a depth of 60 metres in Australia. Belonging to the order Polyzoniida, it was discovered while drilling a hole for mineral exploration.
Millipedes range in size from dwarfs with a body length of 1.4 mm to giants with 30 cm. They are classified into five types based on their body structure: rammers, litter splitters, borers, pill millipedes, and bark dwellers.
Classifications
Rammers, or bulldozers as they are sometimes referred to, belong to the orders Julida, Spirobolida and Spirostreptida. They are long, thin, cylindrical, and use their heads like a bulldozer to push through leaf litter. Their numerous legs provide the force to push through soil and litter. Spirostreptids range in size from the largest millipedes to the smallest. They are adapted to live in various types of biomes—rain forests, grasslands, deserts and caves.
The Spirobolid species, on the other hand, appears uniformly similar and it is difficult to identify the species from their external characteristics. They are predominantly tropical in distribution. Julids show considerable diversity in form and body structure and are well distributed in the Neotropical regions.
Wedge or litter splitters, also known as plate millipedes, are the most diverse Indian species in the order Polydesmida. These are short millipedes with 18-21 segments. Each segment has a laterally expanded projection called keel that gives it a flattened appearance. The keel assists the millipede in movement. Some species have pores on their bodies from which they release irritant chemicals such as hydrogen cyanide and formic acid. These are released slowly, and in some rare cases sprayed out.
Being detritivores (feeding on dead organic material), millipedes are also found to reside in caves, specially adapted to the troglobitic (bound to underground habitats) way of life. A blind millipede, Typhlopygmaeosoma hazeltonae, belonging to the order Polydesmida, was discovered from a cave near Shimla. Whereas 100 species of cave dwellers have been discovered in China, only one cave dweller has been described in India. Clearly, millipede studies have not taken off in India, despite them being an ecologically important group.
Millipedes of the order Chordeumatida and Colobognatha are commonly called borers. These too are small in size with free sternites and tergites (segments of the body). They have narrow, pointed heads with successive segments larger than the previous one. This arrangement with a tapering anterior region helps them in forward movement and soil penetration. They suck nutrients from rotting vegetation.
Pill millipedes or rollers do just what their name suggests—roll into a neat ball when a threat is perceived. They do not roll into a wheel as is noticed among bulldozers, but into a tightly shut ball. A locking mechanism ensures that they cannot be prised open unless you harm them. That is why they are also known as ball millipedes. When you hold them in your hand, they are like a small ball or soft stone. Leave them alone for some time and you can see them unroll themselves. This is also a protective mechanism to reduce water loss by reducing the surface area exposed to air.
They belong either to the order Glomerida or Sphaerotheriida. The former has 12 body segments, whereas the latter has 13, which is one of the characteristics to identify them. Glomerida are generally found in north India, whereas Sphaerotheriida are found throughout India although predominantly they are a south Indian species. The giant pill millipedes of the genus Arthosphaera are endemic to south India. These are used in producing millicompost.
Bark dwellers or bristle millipedes live under the barks of trees. These are more common in tropical regions, are quite small, and have a distinct appearance as their soft body is covered with setae (bristles). At first sight they can be mistaken to be the larvae of the dermestid beetle. Their legs are used only for walking and, unlike in other millipedes, are not modified for mating or sperm transfer. Since they are small—less than 5mm long—with a soft body bereft of the hard exoskeleton, and produce no chemicals for defence, they use their bristles to defend themselves. When threatened by a predator, the sharp, barbed bristles are detached from the body and get entangled in the mouth or body parts of the predator, giving them time to escape. They belong to the order Polyxenida. The researchers Sergei Golovatch and Thomas Wesener 1 report eight species of bark dwellers from south India, of which Unixenus padmanabhai and Silvestrus seminudus occur in the southern Western Ghats region.
Ecological importance
Millipedes prefer environments with constant to high moisture levels and moderate temperatures. They are therefore abundantly distributed—both in terms of numbers and diversity—in the tropical and subtropical regions of the world. While most are predominantly forest-floor/soil dwellers, some of them climb trees to reside in crevices to feed and escape the heat.
More than tigers and other large carnivores, millipedes are among the ecologically significant invertebrates whose presence helps conserve nature. How are they ecologically significant? One reason is that they are mulch-munchers. In modern parlance, you could say they are in the business of waste disposal.
They are efficient as mechanical decomposers of wood and leaf litter. In fact, they are the leaders of the pack of invertebrates that break down wood and leaves and increase soil mineralisation. As detritivores, they contribute indirectly to the decomposition of soil ‘wastes’. Their feeding stimulates microbial activity in plant material which releases chemical nutrients into the soil.
The researchers J.M. Anderson and D.E. Bignell have reported that plant material passing through the gut of millipedes can help in the establishment of soil bacteria. According to the researchers, although millipedes feed on only 10 per cent of the total leaf litter in an ecosystem, 90 per cent of that litter is broken down because of the microbial activity. This results in the redistribution of organic materials and an increase in elements such as nitrogen, making the soil healthy. Millipedes’ preference for certain types of decaying litter is closely related to the nitrogen, carbohydrate and moisture content in it. They prefer leaves with a higher concentration of sugars and low concentrations of polyphenols.
An analysis of the digestive tract of Anoplodesmus splendidus has revealed the presence of a variety of bacteria and fungi 2 in it. While the stomodaeum (anterior part of the gut) was populated by bacteria, the proctodaeum (posterior part) was host to fungal population.
Microbial population in the gut of several other millipede species has also been recorded. A recent discovery has been the fungal association with a species of Colobognatha . It was found that wood-decaying fungi served as a primary food source for the fungivorous millipede, Brachycybe lecontii .
Millicompost
Millipedes contribute not only to soil formation but also to its physiological and chemical properties. Composting using millipedes has been discovered to be a boon for organic farming and improving soil health. 3
Millicompost was first attempted using the giant pill millipede Arthosphaera magna in 2002. Subsequent trials by various researchers confirmed the superior quality of millicompost and its beneficial effect on plant growth. Yet it is still in its infancy, failing to capture the attention of farmers or promoters of organic agriculture.
Studies have shown that millipede composting yields a richer end product than vermicomposting. A comparative study 4 of compost produced from flower wastes using the earthworm Eisenia fetida and the millipede Arthosphaera magna showed that the content of nitrogen, phosphorus, potassium and calcium was higher in millicompost.
The research also studied the effect of these composts on various growth parameters of Capsicum annum , such as plant height, number and area of leaves, number of fruits produced, and chlorophyll content. All these parameters showed a much better result when grown with millicompost than vermicompost.
The Anoplodesmus species, Orthomorpha coarctata and Xenobolus carnifex that are common in India can also be used to produce compost. However, there is a word of caution. Some of them start feeding on newly sprouted seedlings if they run out of leaf litter. At a time when soil health is a concern to farmers, millipede composting deserves more attention.
Tummy doctor for lemurs
The ecological significance of millipedes extends beyond soil health. Several life forms in the wild have discovered that millipedes cure their digestive problems. Louise Peckre and her colleagues from the German Primate Centre in Gottingen observed that the red-fronted lemurs of Madagascar chewed on freshly emerged millipedes after the first rain of the season. Large quantities of an orange-coloured substance were thus produced. The lemurs rubbed this orange secretion around their anuses, tails and genitals.
The chemical benzoquinone, secreted by millipedes, is a mosquito repellent. It helped the lemurs get rid of worms, among them pinworms and their eggs around the anus.
The researchers noticed that the lemurs also consumed a large number of millipedes. The millipede secretions also help cleanse the parasites found in their stomachs and intestines. According to the researchers, the lemurs consumed millipedes both as a curative and as a preventive measure.
Millipedes secrete a variety of chemicals to ward off predators. Such chemicals are repellents, irritants, sedatives or toxic substances. Opossums, meerkats, striped skunks, capuchin monkeys and some bird species consume or use millipedes or their secretions to protect themselves.
Recently, Henrik Enghoff 5 of the Natural History Museum, Denmark, and colleagues found that the Bobo people of Burkina Faso consume millipedes as food. They eat the flatbacked and cylindrical millipede species that are endemic to that region. These species are rich in unsaturated fatty acids, calcium and iron.
Burkino Faso is home to several species of the malarial parasite plasmodium. The benzoquinone from millipedes help serve as insect repellents. The ingestion of the cyanide (produced in sublethal quantities) is also believed to build resistance to malaria. According to the researchers, “…ethological and bioanthropological evidences suggest that ‘toxic’ millipedes consumed by the Bobo people take part in a complex biocultural mechanism for malaria control”.
Eight-year periodic millipede
Interesting discoveries about millipedes continuously emanate from South Asian countries. Since 1920, train operators in Japan have observed that swarms of millipedes periodically descended on to the tracks in the thick, forested mountains in Honshu, forcing the trains to halt 6 . Then, as mysteriously as they arrived, they would disappear, not to be seen for another eight years.
Scientists solved this mystery in the 1970s.
The “train-millipedes”, as they are known locally, are endemic to Japan. Like cicadas and bamboo, they too have an eight-year life cycle. The findings by scientists matched the observations by train drivers, who would keep records of their swarming, as it was impossible to even walk through as the millipedes formed a dense blanket over the rails. Professors from Shizuko University painstakingly collected historical records and determined their life stages to solve the mystery. They discovered a synchronisation between multiple broods. Each brood completed its life cycle in eight years. It took seven years from the laying of eggs to become an adult, which always emerged in summer.
Why did they appear on the tracks? In search of food. All millipedes need dead and decaying leaves to survive. Once they clean up all the available leaves at the site of their birth, they move in search of new pastures, and the train track happens to be in their path. When the adults have had their fill, they mate, lay eggs and die. The nymphs live inside the soil, and only the emerging adults get noticed. Periodic swarming of millipedes in such large numbers is yet to be observed elsewhere.
Centipedes
An account of millipedes would be incomplete without mentioning centipedes, with whom they are often mistaken. Just as millipedes are said to have a thousand legs, the centipedes are mistakenly believed to have a hundred legs.
Centipedes belong to the order Chilopoda. Unlike millipedes, they have only one pair of legs in a segment. This is one way of distinguishing them from millipedes.
Centipedes are carnivorous, and their bite carries a venom that can harm humans. They too are found in the soil, but unlike millipedes that laze about in the soil, centipedes are quick movers. They hide below stones, wood or any rotting material, and when discovered move fast in search of another hiding place. The languorous movement of a millipede is in contrast to the darting movement of centipedes.
Despite being venomous, the centipede finds mention in many cultures. For Koreans it is a sign of good luck and wealth. The Korean word for centipede translates to ‘money bag’.
The centipede carries deep symbolism in Asian cultures. Considered to have healing powers, it is an important component in traditional Chinese medicine. It is a lucky charm in Feng Shui.
Ancient Egyptians, noticing that the centipede fed on insects that attacked dead bodies, worshipped Sepa or the Centipede of Horus. They believed that the centipede had powers to subdue venomous creatures. Sepa was often called upon to protect against scorpions and snakes.
Millipedes, on the other hand, were the favourite of African people who kept giant millipedes as pets. They believed that it brought them good luck. Gamblers would carry millipedes with them to increase their chances of winning bets.
Charm or not, conserving millipedes has a lot of advantages. The first step is to get to know the many species in one’s country; millipede taxonomy is just beginning to attract researchers. The next is to study their life histories. The fact that a millipede could survive at 60m below ground shows how humans know very little about the diversity of small forms, where they reside or what they do. The only way to ensure that we do not lose millipede diversity is to stop habitat destruction. Millipedes help conserve soil and, by extension, the terrestrial habitat. They are important components of the forest ecosystem, and their lifestyle can be a boon to farmers in search of alternatives to chemicals. The animal world uses them as insect repellents. Do we need more reasons to protect them? A millipede movement is the need of the hour .
Endnotes
1. Sergei I. Golovatch & Thomas Wesener: Monograph-A species checklist of the millipedes (Myriapoda, Diplopoda) of India. Zootaxa 4129 (1): 001–075 http://doi.org/10.11646/zootaxa.4129.1.1
2. Bano, Kubra,Bagyaraj D.J. & Krishnamurthy R.V.: Feeding activity of the millipede, Jonespeltis splendidus and soil humification. National Academy of Sciences, India, Vol. 83B, No. 1, 1976, pp. 1-11
3. Ashwini K.M. & Sridhar K.R.: Towards Organic farming with millipede Arthosphaera magna. Current Science , Vol. 82, No.1, 10 January 2002. Pages 20-22.
4. Ramanathan B. & Alagesan P.: Evaluation of millicompost versus vermicompost. Current Science , Vol. 103, No. 2, 25 July 2012. Pages 140-143.
5. Enghoff,H. et al: Millipedes as Food for Humans: Their Nutritional and Possible Antimalarial Value—A First Report. Hindawi Publishing Corporation, Volume 2014, Article ID 651768,9pages.http://dx.doi.org/10.1155/2014/651768
6. https://www.globalsoilbiodiversity.org/blog-beneath-our-feet/2016/8/29/the-periodical-millipede-parafontaria-laminata-armigera
