Bare paddocks or stubble paddocks are unsuitable for webworm development. Some shade is essential for the small eggs to avoid overheating and drying up. When the young caterpillars emerge, they are prone to starvation and shrivelling up. They have to find grasses growing from autumn rains. Moist conditions and undisturbed paddocks provide the best conditions for webworm and may allow hundreds of caterpillars per square metre to survive.
Large numbers are often present in pasture but usually go unnoticed.
Minimum tillage methods allow a high survival rate whereas weed control and soil disturbance reduce or eliminate the pest population. The name webworm refers to several moth species which grow to between 1 cm and 2 cm long. They are straw coloured and distinguishable from each other by the patterns on their wings which are folded closely along their body when at rest. In autumn, but especially in April, these moths may be seen flying at night or they may be disturbed from grassy areas. The eggs are rarely seen as they are only half a millimetre long and are scattered on the ground in grassy areas.