Sentence:  Earless <WSD>ghost</WSD> swift moths become “invisible” to echolocating bats by forming mating clusters close (less than half a meter) above vegetation and effectively blending into the clutter of echoes that the bat receives from the leaves and stems around them. 
Meaning of the word marked with <WSD> tags:  Any faint shadowy semblance; an unsubstantial image