Redback spiders quietly spread near Ennore

Chennai: A venomous spider known for its medically significant bite may be quietly establishing itself on the city’s northern edge in Ennore Creek, an ecologically sensitive area that has faced significant degradation in recent years. A group of researchers identified and recorded redback spiders (Latrodectus hasselti Thorell), also called the Australian black widow, in an old fly-ash dump pond surrounded by salt marsh and grassland habitats. The observation was made in Oct 2025 during a survey of flora and fauna diversity.

Researchers said this is the first record of the species in the city and the first from a coastal lowland habitat in Tamil Nadu. The spider was first identified in the state in Coimbatore and later reported from Madurai and Kiluvamalai in the Eastern Ghats. Native to Australia, the species has spread to other regions, including southeast Asia and New Zealand.

“The population appears established with multiple adult females bearing egg sacs and at least one adult male recorded,” said M Anbarashan, corresponding author of the study, a multi-institutional effort involving the French Institute of Pondicherry and the University of Madras, published in Zoo’s Print journal.

Researchers said the warm, dry and disturbed conditions of the decommissioned fly-ash pond may favour the spider, while surrounding salt-marsh vegetation points to an ability to adapt to coastal estuarine environments.

Widow spiders belonging to the genus Latrodectus are found worldwide and are known for their potent venom and impact on human health, researchers said. Studies state the venom contains latrotoxin, a neurotoxin that attacks the nervous system, making bites medically significant because they can cause intense pain, sweating, nausea, muscle spasms, and, in some cases, widespread symptoms if untreated. Several previous studies have shown that only adult female Latrodectus hasselti have fangs long enough and venom potent enough to be dangerous to humans, while males are harmless. Fatalities are rare since the development of an antivenom in the 1950s.

Until now, the species in south India was largely recorded from hilly regions in the Western and Eastern Ghats, including Coimbatore, Madurai and parts of Telangana. Ennore Creek, the researchers said, represents a significant shift in habitat, with its mangroves, mudflats and backwater system altered by industrial activities.

“Previously, the species was seen only in hilly regions; this is the first time it has been documented in a low-lying coastal plain,” said P Sridhar, co-author of the study.

The authors stressed the need for more field surveys to determine whether the sighting is isolated or signals a broader spread. “Targeted surveys of similar industrial coastal habitats in peninsular India are needed to determine whether this occurrence represents an isolated introduction or part of a broader coastal range expansion,” said K Ilangovan, co-author of the study.