<-unit 0 "moveSpeed" .5 SetScriptVar
The above does not work as expected for dynamically generated runner's nests.
Check to see how moveSpeed is initially declared (if at all) in the script you are setting it in.
$moveSpeed:1
and
$moveSpeed:1.0
Will declare one as an integer type and the other as a float type.
It is in pixels per frame, not per second as it states in the reference as far as I can tell. Setting the same setting manually allows you to specify a fractional number.
I'd guess that it's like emitters, spore towers, &c where the number you have to set it to is 1,000,000 (might be a different number) times the value it shows in the editor dialogue, although I could very well be completely incorrect.
I already tested that particular hypothesis. The number you give to runners nests is the same as the number that appears in the nest settings menu. Provided it is an integer.