There appear to be two possible origins for the name Hemaris:
1-From the Greek hemera, meaning a day(1), possibly referring to the day-flying habits (PDF factsheet on Hemaris tityus, a European species).
2-From the Greek root haem, meaning blood. North American species of Hemaris were originally placed in the genus Haemorrhagia Grote (2), clearly from the root haem. This suggests some sort of relationship, though the spelling, one would think, should have been something like haemaris!
Numbers
4 species in North America listed at All-Leps: diffinis, gracilis, senta, thysbe
adults are easy to identify to genus level due to their habit of hovering around flowers like bumblebees; see individual species pages for identification to species level
Range
represented throughout North America, including the Arctic
