Complex sentence: Moths like hawk moths or larger Saturniid moths lack ears and show no response to ultrasound stimuli, most probably because they are too big for the average bat and have no survival advantage from auditory warning measures.
Split into simpler sentences: Moths like hawk moths or larger Saturniid moths lack ears and show no response to ultrasound stimuli. This is because they are too big for the average bat and have no survival advantage from auditory warning measures.