Which of the following is a key factor in identifying insects from the order Lepidoptera?

The key factor in identifying insects from the order Lepidoptera is their wings, which are covered in scales. Lepidoptera, which includes butterflies and moths, is characterized by this unique feature that differentiates them from other insect orders. The scales can create vibrant colors and patterns, which not only serve aesthetic purposes but can also facilitate thermoregulation and reduce water loss. Scales are critical for their functionality in flight, as they help provide lift and reduce drag.

The variations in wing scaling patterns are often used for species identification, making it an essential characteristic in their classification. This defining feature of having scaly wings is unique to Lepidoptera, thus, it is a primary factor in their identification.