Because moths are such a large group, interested amateurs can contribute useful information. Take the moth above, the Deep Yellow Euchlaenia (Euchlaena amoenaria). This moth is fairly common and widespread through eastern North America, as one can see from the map at the Moth Photographers Group. Despite this, it seems that its larval host plant is still unknown, and there are no images of caterpillars for this species at either BugGuide or MPG. Many other species lack complete range information.
Even though this is a common and widespread moth, I was excited to see this land on my sheet last Wednesday since it was a new species for me.