Caterpillars march in large numbers in the evening hours and feed on the leaves of paddy seedlings till the morning and hide during daytime. They feed gregariously and after feeding the plants in one field march onto the next field. Under severe infestation crop gives the appearance of grazed plants. Attacked plants are reduced to stumps. Nurseries situated in ill-drained marshy areas are attacked earlier than dry ground. Damage is severe during July to September. After finishing the crop of one field the swarm marches to another field in a regular army formation manner,hence this insec-pest is also called as "Army warm".