Dynastes neptunus is rather similar in form to the somewhat larger D. hercules, but its body is black instead of brown.  Also, the horns are more slender and often much more curving than in D. hercules, and the cephalic horn is of similar length to the thoracic one.  Additionally, there are two lesser yet very pronounced horizontal horns parallel to the base of the thoracic horn.  D. neptunus had a reputation as being a very rare beetle for many years, but that was before it was discovered that it mainly only emerges from hiding just before dawn, and perhaps that is why it was not frequently seen previously.  It is now known to be quite common in the rain forests throughout much of the northwestern portion of South America.