The Ditrysia are a natural group or clade of insects in the Lepidopteran order. It contains both butterflies and moths. They are called ditrisians because the female has two distinct sexual openings: one for mating, and the other for laying eggs.
About 98% of described species of Lepidoptera belong to Ditrysia. The group can be divided into basal or incertae sedis "micromoths", and the Apoditrysia. The Apoditrysia includes mostly the larger moths and the butterflies.