Centipedes have been crawling on earth for more than 420 million years. To give some perspective, the genus Homo to which we belong has been on earth for only around 2 to 2.5 million years. Among arthropods (animals with jointed appendages), which include insects (e.g. beetles, butterflies), spiders, crabs, and other animals, centipedes stand out because of their long bodies with numerous segments and multiple legs. The closely related millipedes, which also have long, segmented bodies and multiple legs, can be distinguished from centipedes by closely observing the number of legs in each segment – in millipedes, there are two pairs of legs in each segment, while in centipedes, there is only one pair per segment. This body plan of centipedes hasn’t changed much since the last 400 million years, and therefore they are also referred to as ‘living fossils’. In fact, studying such ancient animals can also give us a clue about how arthropods moved from the marine habitats in which their ancestors were found, to terrestrial habitats.
Centipedes are found in all the continents of the world except Antarctica. More than 3100 species of centipedes are currently known to science. New species continue to be discovered across the world, occupying diverse habitats such as dry scrub forests, savannahs, evergreen forests in tropics, and even temperate forests at higher latitudes. Centipedes prefer cool and moist places and are often found in leaf litter, under stones, and in gaps of barks. Interestingly, they also often live and breed among ferns on tree trunks, up where the temperature inside the fern can be almost six degrees cooler than the ambient temperature.
While some centipedes can be as long as 30 cm (e.g. Scolopendra hardwickei –Tiger Centipede) there are others that are only a few centimetres long (4 cm). While most centipedes appear black or brown, some can be colourful: bright red, orange, deep blue, or sky blue. While some centipedes have clusters of ocelli or eyes, some are blind. Centipedes play the role of tigers in the invertebrate world. Like many carnivorous animals, centipedes are solitary and nocturnal.
Unlike millipedes, centipedes are often feared because they are venomous. Interestingly, the first pair of legs of centipedes is modified into claws that have the venom gland. Venom is important for centipedes to decapitate their prey, which include invertebrates like insects, arthropods and earthworms, and occasionally vertebrates like lizards, bats and snakes. On the other hand, millipedes feed on mostly dead and decaying matter. Centipedes get predated by birds, snakes, and sometimes even by spiders and scorpions.
Centipedes may lay eggs or give birth to young ones. They exhibit parental care, and the female may be seen carrying its young between its rear legs. They can be cannibalistic, like other carnivorous arthropods like spiders.
I was fascinated by centipedes when I first started looking for them in the forests of the Western Ghats in Maharashtra. At that time, I was asking a modest question – how many different centipede species are found in the different habitats of the northern Western Ghats? Later in my doctoral and post-doctoral research, I not only studied the number of species found in an area, but also how they came into being in the first place. Immediately after my Master’s, I joined Indian Institute of Science, Bangalore, for my PhD under the supervision of Dr. Praveen Karanth. In Dr. Karanth’s lab, I studied and learnt about evolutionary biogeography and started to use molecular tools (DNA-based analysis) to systematically document the diversity of scolopendrid centipedes in the Western Ghats.
During my time at Natural History Museum, London, I studied centipede morphology in detail. I looked at the original descriptions of many species, compared the Western Ghats centipedes with global collections, and learnt a lot about centipede fossils from my post-doc advisor Dr. Gregory Edgecombe. DNA sequences along with morphological data are a useful way to identify species. This is especially relevant in the case of centipedes, as I found that different species of centipedes look morphologically very similar, and only when we examine their DNA can their species identity be established. In the last ten years, using DNA sequence and morphology data, I have found 11 new species of centipedes and rediscovered a few after almost 100-150 years. Interestingly, most of these species are endemic to the forests of Western Ghats.
Once the evolutionary relationships among species are known, this can be very helpful to elucidate the process of species’ origins. The Western Ghats of peninsular India was part of the Gondwana landmass, 200 million years ago. Gondwana landmass comprised of present-day South America, Africa, Madagascar, Seychelles, peninsular India, Australia and Antarctica. Peninsular India sequentially broke away from South America, Africa, Australia and Antarctica, Madagascar, and lastly from Seychelles between 200–66 million years ago. The peninsular Indian plate moved north-eastwards towards Asia and collided with the Eurasian landmass approximately 50 million years ago. Because of this complex geological history, currently, we have taxa (animals and plants) in peninsular India whose closest relatives are from either Gondwana, Eurasia (comprising of Europe, North Asia and South-east Asia), or taxa which have evolved on the drifting peninsular Indian plate.
I wanted to understand whether centipedes were there on the moving Indian plate or if they arrived in peninsular India and the Western Ghats from Asia after the Indian plate collided with Asia. Using molecular phylogenetic and time estimation tools, I was able to establish that centipedes in the Western Ghats were present at least 80-100 million years ago, suggesting that the ancestors of the current centipede species were present on the moving peninsular Indian plate. Very few animal groups that are found in the Western Ghats are known to have such ancient history.
I also found that the mountains of Agasthyamalai Hills harboured the highest diversity of centipedes. Their diversity and evolution in the Western Ghats were strongly influenced by yet another big geological event – the Deccan volcanism. The northern and central portions of the Western Ghats experienced a lot of volcanic activity approximately 65 million years ago. It was only after this volcanic activity subsided, and again the tropical climate and forests were established, that the ancestors of the extant centipede species dispersed from southern to the northern and central parts of the Western Ghats. So, the southern Western Ghats, which had experienced little or no volcanic activity, had served as a refuge for these centipedes!
The Western Ghats are home to four orders of centipedes – Scolopendromorpha, Geophilomorpha, Lithobiomorpha, and Scutigeromorpha, with hundreds of species. For the past 10-12 years, I have been studying just one family – Scolopendridae. The remaining families and orders are yet to be studied and several new species remain to be discovered!
While these studies continue, the forests of the Western Ghats and other tropical areas across the globe are under immense pressure from anthropogenic activities that result in the loss and fragmentation of these forests. The impacts of these activities on centipedes and other lesser-known vertebrate groups are poorly understood. It is tragic that one species (humans) can potentially pose such a grave threat to other species that have existed on earth for significantly more millions of years!