In ‘landmark’ find for forensics, ZSI IDs 17 distinct blow fly species
Times of India | 20 August 2025
Kolkata: A breakthrough study by Zoological Survey of India (ZSI) on blow flies promises to transform forensic investigation by helping scientists accurately determine the time of death, especially in the case of decomposing bodies.
Led by ZSI director Dhriti Banerjee and scientist Atanu Naskar, researchers collected 2,977 specimens from four regions of Bengal and identified 17 distinct blow fly species, each with its own genetic signature. Their analysis found significant genetic differences between species (up to 12.3%), ensuring definitive identification.
Blow flies are among the first insects to colonise a corpse and are crucial in estimating the postmortem interval or the time elapsed since death. Traditionally, forensic scientists relied on the size and growth stages of the insects — an approach prone to errors, as different species vary in size, characteristics and infestation periods.
"This is a game-changer for PMI estimation," said Banerjee. "With DNA barcoding, species identification can happen within hours — even from a single egg — without waiting for the maggots to mature, significantly boosting accuracy and speed," she added.
"Different species of blow flies have different larvae size and growth rate. But since many blow fly species look alike in their early forms, misidentifications led to inaccuracies in determining their age, and hence, how old the corpse was. The ZSI team overcame this by focusing on a tiny mitochondrial gene segment — Cytochrome Oxidase I — known as the ‘DNA barcode'," explained Banerjee.
The findings were validated using four globally recognised scientific methods, all confirming that each species forms a distinct genetic cluster. This makes the blow fly's DNA an indisputable forensic marker. The study has been published in the international journal PLOS ONE.
"Forensic science has long focused on human evidence," Naskar explained. "But nature itself provides vital testimony. The fly's DNA speaks volumes," he added.