On the trail of a lost relic [Commentary]

As entomologists, we spend countless hours in the field, meticulously observing and collecting data on insects. Yet, every so often, nature rewards our patience with some unexpected discovery, one that offers a rare glimpse into its hidden secrets. An expedition to Siang Valley did just that – it led to the rediscovery of a long-lost velvet worm (Onychophora) after more than a century.

Nestled within the Himalayan biodiversity hotspot, Arunachal Pradesh’s Siang Valley showcases an unparalleled wealth of diversity. The valley’s lush greenery is home to elusive wildlife and countless insects, while the rhythmic sounds of the forest and the river’s roar create an enchanting symphony. Indigenous communities have coexisted with this wilderness for centuries, adding cultural depth to its ecological richness. A place of raw beauty and scientific wonder, Siang Valley remains one of India’s great frontiers, where nature’s secrets are still waiting to be unveiled.

The early ‘Abor Expedition’ to the Siang Valley, in 1911–1912, during the period of colonial rule, was originally a punitive military campaign, launched by the British in response to the killing of Noel Williamson, a British political officer, by the indigenous people there. This resulted in the Anglo-Abor Wars (1911-1912), a series of conflicts between the Adi tribes and the British forces. Recognising the valley’s untapped ecological wealth, a scientific expedition was launched alongside military operations to systematically document the Siang Valley’s natural history and geographical features. This expedition resulted in the collection of numerous biological specimens, including the first recorded specimen of velvet worm Typhloperipatus williamsoni from South Asia, described by the zoologist Stanley Kemp in 1913.

Over a century later, our team of researchers took a series of expeditions under the banner “Siang Expedition,” funded by the National Geographic Society through the wildlife-conservation expedition grant, to resurvey the biodiversity of the region. These expeditions conducted by our team during 2021 (April), 2022 (April–May), and 2023 (May) contributed thousands of plants and animal specimens belonging to various orders and families.

Read more: Retracing the route of a century-old biodiversity expedition

During one of these expeditions, our team started a trek on May 17, 2023, from the Yingku village community censer in the East Siang district, assisted by our field assistant, Talem Mize. We headed into the eastern forests. After a long trek spent setting traps and collecting insects, our team was making its way back when our senior researcher, Priyadarsanan Dharma Rajan, suddenly stopped. He gazed upward at an enormous tree—so tall and straight it emerged far from the canopy, its roots hidden from our view. Noticing our curiosity, our field assistant gestured toward a deep slope and said, “The base is down there”. With his trademark curiosity sparkling in his eyes, Priyan declared. ‘Let’s go see what’s hiding underneath!”  Without hesitation, we decided to set forth expecting some surprises hiding there. The treacherous, steep terrain forced us to slide and tumble multiple times. After much slipping and falling, we finally reached the base of the towering tree. From that vantage point, however, its top was lost in the dense canopy above, and our feet were struggling to get a hold.

The place was rich in leaf litter, exactly what we were hoping for. For an entomologist, a deep, untouched leaf litter bed is endless possibilities waiting to be explored. Excited, we got to work immediately, aspirator in hand, scanning every crevice for insects. I spotted a few Crematogaster ants, but as soon as I collected one, the others disappeared. Determined to find more, I lifted fallen logs, overturned rocks, and sifted through the litter.

Then, under one boulder, I saw an unfamiliar worm-like creature crawling slowly. There’s a unique thrill in discovering something completely unexpected. In that moment, I couldn’t call anyone; I was too engrossed, too cautious not to lose sight of it. Usually, when I miss a specimen, it endures in my mind for days. That too; this was something far more special. It was a velvet worm.

The tiny creature moved beautifully, its segmented body and numerous legs gliding across the damp earth. It was a juvenile, pink in colour, waving its delicate antennae as it tried to burrow back into the mud. Carefully, I collected it, shaking hands with excitement. Sensing danger, it spurted a white mucus thread in self-defence. This sticky, proteinaceous secretion is to entangle prey and then deliver a venomous bite; this behaviour accounts for their alternative name, spitting worms.

We had just found a velvet worm, Typhloperipatus williamsoni.

Velvet worms are an ancient and cryptic group of soil-dwelling invertebrates that share traits with both arthropods and tardigrades (water bears)- a phylum of eight-legged segmented micro-animals known from deep seas to mountaintops. Velvet worms were once believed to be sisters to annelids and arthropods. Like annelids, they have a soft, metameric segmented body, while their arthropod-like features include the presence of a cuticle, a central blood vessel, and flexible, unjointed legs that can move in different ways. Known as ‘living fossils,’ velvet worms have a rich evolutionary history, offering valuable insights into the early evolution of land animals.

The rediscovery of velvet worms is ecologically and scientifically profound. These ancient, elusive invertebrates provide unique insights into evolutionary biology, biodiversity, and ecosystem health. Because they are habitat specialists with little ability to disperse, their presence is a sign of rich, undisturbed forests. Each new specimen offers more opportunities for molecular and morphological studies that help clarify species boundaries, evolutionary relationships, and biogeographic histories, tracing continental drift, speciation, and lineage diversification. Such rediscoveries not only deepen our understanding of hidden biodiversity but also provide critical data for conservation and evolutionary research.

That Typhloperipatus williamsoni remained unseen for over a century underscores just how difficult velvet worms are to study. Their nocturnal, leaf-litter-dwelling lifestyle, combined with extremely restricted ranges and small populations, makes them hard to spot even during intensive surveys. Historically, they have also received little research attention compared to more charismatic or economically important species. Adding to this challenge, many of their habitats are remote, underexplored, or threatened.

Protecting these hidden evolutionary relics demands urgent habitat conservation, targeted research, and greater public awareness. Without such action, ancient lineages like Typhloperipatus williamsoni may disappear before we can fully understand their role in ecosystems.

The author is a researcher at the Insect Biosystematics and Conservation Laboratory, ATREE Bangalore.

Banner image: An expedition to Siang Valley led to the rediscovery of a long-lost velvet worm after more than a century. Image by Sahanashree Ramakrishnaiah.