Poplar hawk-moth caterpillar (Laothoe populi). Caterpillars are the larval forms of moths and butterflies. They feed on leaves and then metamorphose into the adult form. Caterpillars can be brightly coloured, with patterns such as the red spots seen here. This is thought to help protect against predators. This hawk-moth is common in the UK, with the adults seen from May to July. The caterpillars feed on the leaves of the poplar, aspen and willow trees. This caterpillar has a yellow-green spike, instead of the blue-green spike of the eyed hawk-moth caterpillar.