The Tyranids are looking to find every bit of biomass they can in the galaxy and add it to their hive. That's the goal of their crusade, and we get a look at how that works with their Crusade rules coming in their new codex.
From the article:
There’s a Shadow in the Warp, and it heralds the imminent arrival of Codex: Tyranids on pre-order this weekend. The big bugs have gotten even bigger, Synaptic Imperatives have made Synapse creatures even more pivotal, and hive fleets are packing a new biomorph known as the Parasite of Mortrex. The sound of mandibles clicking is deafening, and it’s time for a celebratory feast.*
Codex: Tyranids still has more secrets hidden under its chitin, however – such as Crusade rules all about scoping the galaxy for the latest tasty morsels.