Wednesday, June 12, 2013

Millipedes (Phylum Arthropoda: Class Diplopoda) of Singapore

Millipedes (phylum Arthropoda, subphylum Myriapoda, class Diplopoda) are easily recognised by their long segmented body with two pairs of legs on most segments, except for the first few and last segments. The name means "a thousand legs", but while there are species in the world with more than 700 legs, the ones seen in Singapore seldom have more than 100. They are from the subphylum Myriapoda, which typically comprises elongate arthropods which possess numerous pairs of legs ("myriapoda" means "10,000 legs" in ancient Greek), a trunk with many segments, and a head with one pair each of mandibles and antennae at the front end.

Like other arthropods, they have jointed legs ("arthropoda" means "jointed legs" in ancient Greek), a bilaterally symmetrical body, and a tough exoskeleton (or external skeleton) composed largely of a tough material called chitin. As they grow, they need to moult, i.e. discard the old skeleton and grow a new one. Their cuticle (i.e. outer covering) is not waterproof, and hence they are largely terrestrial. Most species are also nocturnal to avoid water loss, and are most readily found in damp habitats such as the leaf litter or underground. They can breathe by taking in air through openings in the cuticle.

Most species feed on decaying organic matter or fungi, and hence they are commonly seen in the leaf litter or on fallen trees. They are not venomous, and protect themselves either by secreting toxic or distasteful chemicals, or roll up to protect their softer underparts, exposing only the tougher upperparts. To breed, the males usually twist their bodies around the females to transfer the sperm, and the females will lay the eggs inside a nest in the soil. The newly hatched millipedes usually have much fewer legs than the adults, and gain more legs and body segments as they moult.

Here are the various groups of millipedes that can be found in Singapore:



A) Order Spirobolida

Spirobolid millipedes generally have cylindrical bodies, and are usually found in leaf litter or under logs. When disturbed, they tend to curl up and secrete toxic chemicals to deter predators. They can be distinguished from other millipedes by having only one (instead of two) pair of legs on the fifth segment. The reproductive organs of the males are within a pouch.

Rusty Millipede (Trigoniulus corallinus)
The Rusty Millipede (Trigoniulus corallinus) is one of the commonest native millipedes that can be encountered in both urban and rural areas in Singapore. It has a reddish, cylindrical body, and often rolls up into a coil when disturbed. The above photo features a mating pair. This species grows to about 5cm long.



B) Order Spirostreptida

Spirostreptid millipedes are usually large cylindrical millipedes with only one pair of reproductive organs. They are mostly found in the tropics, and many species have strong legs to climb up trees. When disturbed, they can secrete toxic or distasteful chemicals through pores on their sides to deter predators.

Giant Millipede (Thyropygus sp.)
This dark red Giant Millipede (Thyropygus sp.) is seen in the forest climbing up a tree. It is about 20cm long.

Giant Millipede (Thyropygus sp.)
This Giant Millipede (Thyropygus sp.) that has black and orange body segments is also about 20cm long.



C) Order Polydesmida

Polydesmid millipedes typically have between 18 to 22 body rings, with 20 rings being the commonest. They are eyeless, and most are able to secrete toxic cyanide to defend themselves against predators. Many species have their body segments which resemble flatten plates, and hence they are often called flat-back millipedes. These species are also commonly called tractor millipedes as the segments resemble the tyre tracks of tractors. Not all polydesmids have this appearance though, and some may come with roundish segments.

Black-and-Yellow Millipede (Anoplodesmus saussurii)
The Black-and-Yellow Millipede (Anoplodesmus saussurii) is another commonly encountered species, but is unfortunately an introduced one, believed to be native to the Indian subcontinent. It probably came with imported plants, and is now very commonly seen in parks and gardens. This species often occurs in high densities, sometimes up to a few hundred individuals in the same area. It grows to about 3cm long, and can be recognised by the shiny black upperparts and yellow rounded structures by the sides. Many millipedes have the same coloration, but are usually less shiny and the structures by the sides are not as rounded.

Polydesmid Millipede
The above unidentified polydesmid millipede has a similar yellow-and-black coloration, but the structures by the sides are pointed instead of being rounded.

Tractor Millipede
The above unidentified species with very flattish segments was seen in the forest.

Polydesmid millipede
The above unidentified polydesmid millipede is usually found on dead logs. It is quite small, not more than 1cm long.

Millipede (Opisthodolichopus scandens)
This arboreal polydesmid millipede is possibly Opisthodolichopus scandens. It has round reddish segments with a dark line on the back. The ones I have seen are about 5cm long.

Millipede (Opisthodolichopus sp.)
This is likely to be a Opisthodolichopus sp., but I am not sure if it is the same species as the previous one as the colours are different.



D) Order Sphaerotheriida

Sphaerotheriid millipedes are commonly called giant pill millipedes as they are generally larger than other pill millipedes of the same super order, Oniscomorpha. Apart from the larger size, they also can be differentiated from other pill millipedes by having 13 body segments, inclusive of the head.

Pill Millipede
Pill millipedes got their common name from the fact that they will roll into a ball (or pill) when disturbed, hence only exposing their tougher backs and hide the softer underparts.

Pill Millipede
The above unidentified pill millipede is about 2cm long.



E) Order Siphonophorida

Members of the order Siphonophorida are characterised by having either a somewhat conical front end with the mouthparts elongated into a long, bird-like beak with reduced mandibles. Their reproductive organs are very simple and leg-like, being derived from the ninth and tenth legs. Little is known about their diet, though scientists deduced from the shapes of their mouthparts that they probably feed on plant materials.


The above photo features a local siphonophorid millipede with the beak-like mouthparts.


It has about 350 legs! In fact, siphonophorid millipedes hold the "world record" for having the most number of legs, with one American species having as many as 750 legs.



F) Order Polyxenida

Members of this order are generally small millipedes of a few millimetres long with their bodies densely covered with tiny bristles-like structures, and hence they are often referred to as bristle millipedes. Unlike most other millipedes, they do not secrete chemicals for defense purposes, but instead brush their bristles against their predators. The barbed bristles will penetrate into the body of the predator, causing great discomfort or even death. Polyxenid millipedes are usually found under rocks, in leaf litter or on logs.

Bristle Millipede (Order Polyxenida)
The above photo features an unidentified bristle millipede about 2-3mm long. Apart from the hair-like bristles covering its body, it has two bundles of long bristles forming a tail-like structure at the rear. It is usually found in the leaf litter in coastal forests.



References
  • Bartlett, T. & J. VanDyk. 2003. BugGuide. Retrieved May 24, 2013, http://bugguide.net.
  • Burnie, D. 2001. Animal. London: Dorling Kindersley. 624 pp.
  • Decker, P. & T. Tertilt. 2012. First records of two introduced millipedes Anoplodesmus saussurii and Chondromorpha xanthotricha (Diplopoda: Polydesmida: Paradoxosomatidae) in Singapore. Nature in Singapore, 5: 141–149.
  • Marek, P., W. Shear & J. Bond. 2012. A redescription of the leggiest animal, the millipede Illacme plenipes, with notes on its natural history and biogeography (Diplopoda, Siphonophorida, Siphonorhinidae). ZooKeys 241 (241): 77–112.
  • McGavin, G. 2000. Dorling Kindersley Handbooks: Insects, spiders and other terrestrial arthropods. London: Dorling Kindersley. 255 pp
  • Ng, P. K .L., R.T. Corlett & H.T.W. Tan (eds.). 2011. Singapore Biodiversity: An Encyclopedia of the Natural Environment and Sustainable Development. Singapore: Editions Didier Millet. 552 pp.
  • Read, H. J. & H. Enghoff. 2009. The order Siphonophorida - A taxonomist’s nightmare? Lessons from a Brazilian collection. Soil Organisms 81: 543-556.

4 comments:

Hazel Li said...

There are lots of this Black-and-Yellow Millipede (Anoplodesmus saussurii) at Pangsua Connector Park, closer to Sungei Kadut Road. I wonder if they are poisonous and if they will go away or just multiply somemore.

Ron Yeo said...

They are generally quite harmless, so don't have to worry too much about them :)

Pat said...

I noticed that Anoplodesmus saussurii (Humbert, 1865) started appearing in large numbers in S'pore in 2007/08, typically at areas of new landscaping in parks & along roadsides where compost is used as a soil mix or mulch cover.

The key element appears to be rich organic matter in the form of fresh compost. For newly-landscaped areas with installed plants but lacking fresh compost, I don't see A. saussurii.

A. saussurii doesn't bite or cause "obvious" physical harm. But if you were to hold one within your palm, it might secrete a toxin (consisting of acid, hydrogen cyanide, etc.) that causes a chemical burn of the skin, known as millipede burn.

The main symptom of millipede burn is superficial but unwashable brownish stain(s) on the skin. For most people, these stains are painless & gradually fade away with time as the skin sloughs off — in my case, a few months for burns caused by A. saussurii toxin. But for sensitive individuals, millipede burns can result in intense itching, burning or blistering of the skin.

Pat said...

From post: "unidentified polydesmid millipede has a similar yellow-and-black coloration, but the structures by the sides are pointed instead of being rounded" [photo]

Looks like the native Orthomorpha murphyi (Hoffman, 1973), which are blackish-brown with distinctly protruding, angled & pointed lateral flanges along both sides of its body. This species can be found at the BTNR & CCNR forests.

* Orthomorpha murphyi (Species ID)

* Revision of the Southeast Asian millipede genus Orthomorpha Bollman, 1893, with the proposal of a new genus (Zookeys, 131: 1–161, Sep 2011)