Meet the caterpillar slug, a potential future invader to India

Purcell’s hunter slug or caterpillar slug, a native to South Africa, has now spread to several parts of India and a new study has predicted that it could soon become an invasive species attacking western and Peninsular India.

The slug — Laevicaulis haroldi — is listed as an endangered species and was first described in 1980. Not much is known about its ecology and according to studies, it entered India around 2010-2012 accidentally, through international trade via Mumbai. Now, there are over 60 records from all over the country. It has been reported to feed on the leaves and bark of mulberry plants. The slug was also sighted on neem trees, papaya, and calotropis plants.

The research team from Ashoka Trust for Research in Ecology and the Environment (ATREE) studied the distribution of the species using data from the India Biodiversity Portal, iNaturalist website, and previous studies.

They also studied future climate change scenarios to decode which places may be vulnerable to the slug attack. “We used two scenarios RCP 2.6 and RCP 8.5 from the Intergovernmental Panel on Climate Change (IPCC). Here, 2.6 is the best-case scenario where we control emissions and limit anthropogenic climate change. On the other hand, 8.5 represents the worst that could happen. We don’t follow any mitigation rules and have a high-risk future in terms of temperature and other climatic conditions,” explains Aravind N.A., corresponding author of the paper recently published in Current Science. He is an Associate Professor at ATREE.

The models predicted that under both climatic scenarios, most parts of Andhra Pradesh, Karnataka, southern parts of Telangana, northeast Tamil Nadu, Gujarat, western Maharashtra, coastal Odisha, West Bengal, and some states in North East India are highly suitable for the slug.

Economic loss

An international study published in March reported that invasive species have cost nearly $1.3 trillion dollars to the global economy since 1970 and an average of $26.8 billion per year. Also, several studies have noted invasive alien species are responsible for the extinction of native and endemic species. “One theory of invasion biology is that these species thrive because they don’t have any major predators in the new region. Predators and prey in a locality evolve together and when a new species arrives, there is no one to eat it and keep a check on it. This is one of the reasons for the uncontrolled spread of invasive species,” adds Dr. Aravind.

The team writes that early detection and control are key for managing newly introduced species before they become invasive. “We need to capitalise on citizen scientists’ potential in locating hitherto unrecorded populations in a short period with limited resources. Awareness needs to be created among the forest managers, agriculturists, horticulturists and farmers to detect, manage and control this newly introduced species. Non-toxic methods of controlling this pest need to be developed. Also, a strict quarantine in the ports should be in place to avoid further introductions,” concludes the paper.

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