Rarely will I be negotiating. And if I do it will normally only be for completely 1 sided reasoning. And even then a host must be sacrificed for communication. 

[quote=Keyguyperson]
Disrupts warp travel and communication? This sounds delightfully horrible for me.
[/quote]

Yeah haha. Colonies go dark only to be found as airless rocks stripped of all resources months later. The only way you would really know the Tyranids were there is if you had fought them before or if a message was somehow left on the world to be found.

Ships cannot escape, and messages cannot be sent out.