After having long been treated as a subspecies of H. diffinis due to difficulty in distinguishing them morphologically, H. aethra was elevated to species status in 2018.

Strecker (1875) described the moth as Macroglossa aethra based on a female specimen from Montreal, identifying it as either a novel species or a "most remarkable aberrant form of Diffinis [sic]".

[4] Schmidt (2009) barcoded the mitochondrial DNA of nominal H. diffinis specimens from eastern Ontario and found them to be two sympatric groups with diverging genes for cytochrome c oxidase.

H. aethra is found in mesic, open deciduous forest, mostly in igneous bedrock plant communities, conditions that likely reflects the requirements of its host.

Generally, aethra adults are slightly larger and more robust, and the dorsal thorax is a richer orange-brown color contrasting strongly with olive-brown dorsolateral stripes.

The reddish-brown scaling on the apex of the forewings is generally larger and brighter red in aethra than diffinis, taking up 50% or more of the R4-R5 cell, and that on the hindwing anal margins is also more extensive.