Biology and feeding potential of Synonycha grandis Thunberg was studied in laboratory. There were five larval instars and life cycle was completed in about 48 days. Both adults and grubs were voracious feeders and devoured more than 500 individuals in a day. The grubs were attacked by an ant predator, Myrmicaria brunnea Saund. and parasitised by Nothoserphus mirabilis Breus.