Devouring Swarm
Devouring Swarm in the Stellaris encyclopedia: Effects:
Devouring Swarm in the game's words
The encyclopedia entry as the game shows it in its tooltips; underlined words open their own entry or page here.
Effects:
Cannot engage in Diplomacy with other empires!
Cannot access the Galactic Market
Has the 'Hunger' casus belli on all other empires
Xeno Pops will always be eaten
Gains 
Society Research from eating 
Xeno Pops
Modifiers:
- Starbase Influence Cost: -50%
- Ship Hull Points: +25%
- Daily Hull Regen: +5%
- Daily Armor Regen: +5%
- Army Damage: +40%
- Research Speed (Biology): +20%
- Ship Build Cost: -25%
- Naval Capacity: +33%
Our Hive Mind exists only to consume and grow stronger. We will collect all available bio-matter and evolve to consume the galaxy!
Source: common/game_concepts (concept_devouring_swarm) and localisation/english, Stellaris Cygnus v4.5.2 (9776).