13 MAR 2014 by ideonexus

 Humans are Terrifying

More seriously, humans do have a number of advantages even among Terrestrial life. Our endurance, shock resistance, and ability to recover from injury is absurdly high compared to almost any other animal. We often use the phrase “healthy as a horse” to connote heartiness - but compared to a human, a horse is as fragile as spun glass. There’s mounting evidence that our primitive ancestors would hunt large prey simply by following it at a walking pace, without sleep or rest, until it died...
   notes

From a forum, why humans make a great monster race for other aliens to fear. Yet to find original reference yet.