Background: The larva of Ariadne merione, commonly known as the Common Castor Butterfly, is a voracious feeder of Ricinus communis (castor plant), significantly reducing crop yield. Due to the scarcity of updated information on its lifecycle and morphometrics, this study was conducted in 2023 to understand its developmental stages and identify vulnerable phases for pest management.&nbsp; 
 
Methods: Eggs collected from the field were reared on castor leaves, monitored daily, and data on lifecycle, growth, and behaviour were recorded and analyzed.&nbsp; 
 
Result: The durations of the egg, first, second, third, fourth, fifth instar, and pupal stages were 2.022&plusmn;0.839, 2.422&plusmn;0.499, 2.156&plusmn;0.475, 2.444&plusmn;0.586, 2.622&plusmn;0.650, 3.867&plusmn;0.786, and 5.500&plusmn;0.762 days, respectively. Morphometric measurements recorded were: Egg-1.261&plusmn;0.134 mm diameter; first instar-2.618&plusmn;0.286 mm length, 0.613&plusmn;0.092 mm width; second instar-4.554&plusmn;0.660 mm length, 1.311&plusmn;0.228 mm width; third instar-8.341&plusmn;1.294 mm length, 2.736&plusmn;0.402 mm width; fourth instar-11.751&plusmn;3.125 mm length, 3.62 &plusmn;0.922 mm width; fifth instar-19.322&plusmn;3.290 mm length, 5.201&plusmn;0.789 mm width; pupa-18.208&plusmn; .095 mm length, 6.347&plusmn;0.320 mm width. The larvae became intensive feeders from the third instar, causing severe damage such as extensive defoliation. Therefore, control measures should be initiated from the neonate stage to minimize yield loss.

Developmental Biology and Morphometric Traits of Ariadne merione Affecting Castor (Ricinus communis)