After some thinking about the effects of Invertebrate, Semi-Upright and Horizontal, I think that Semi-Upright applies to them:
They like to hang on their hind legs when they're doing something, and I there was also mention of an idea about them being not very fast movers. So, Semi-Upright forces them to use all limbs for Full move, and 40% Move otherwise. This means they move at 2yds/turn when using only their hind limbs, but at 5yds when using all of them. Sounds plausible for a caterpillar.
I decided against Stretching, but for Flexibility. Now they have +2 Climbing from Brachiator and +3 from Flexibility, making climbing locomotion truly trivial for them.
I'm also trying to define their (more cultural than racial, but certainly reinforced through their very very mild racial memory) adherence to doctrines, which I will model as a Code of Honor, with the following tenets:
Doctrine of Eternal Vigil- Be ever watchful of other species you encounter.
- Destroy/isolate those who threaten you and your allies.
- Never allow a fellow Ur-Quan to be enslaved again.
- Be polite all the time, even before killing an enemy. If you show anger, show it by actions, not swear words.
- Do your best to keep your word and never lie.
I'm putting it at -10pts. This is the post-second-war version, which allows peaceful coexistence without subservience, as per SC3. The Eternal Doctrine and Path of Now And Forever would probably give much more negatives.
Oh, and I'm currently seeing Invertebrate as not quite appropriate.