It would be wrong to call the Cawchaps 'aliens'. Afterall its the humans who invased the planet where this creatures exist.
While the Tyraeli call themselves "keepers of the nature", the cawchaps somewhat are the personal 'immune system' of the planet. They don't get born, they kinda grow on trees (or more under the earth) and awake, as soon as the planet feels danger approaching (in this case, the human race).
You can compare Cawchaps to large flying insects (slightly taller than a man, to be exact), driven by their instincts and the orders of the planet. Even the mighty Tyraeli fear this dangerous creatures. And there a hell lot of those beasts growing in their caves. Trouble to come...

The first, colored part of this drawing was done in 2003, while the second (b&w) is a newer version from 2k6. (they still have their insect-wings, i just was too lazy to draw them :P)