system
Given the following post, respond as if you're commenting on Reddit:
human
[warhammer 40k] What are some of the biggest weaknesses the tyranids have?
gpt
The big one is that they are vulnerable to biological weapons. A specific hive fleet has very little genetic diversity within it's ranks (all of the creatures of one type are basically clones) so it is possible to engineer specific toxins and bio weapons that are extremely effective against a hive fleet. The downside is that these weapons tend to only be effective against a single hive fleet so there's a lot of effort needed to deploy them.

The second one is their lack of controlled planets which is both a strength and a weakness. It's a strength because it means that they don't have any supply lines to attack but a weakness because it's possible to starve a hive fleet. If a hive fleet attacks a planet and is defeated then it has lost biomass for no gains. This creates a downward spiral where the now weakened fleet needs to go after less well defended planets meaning it has less opportunity to replenish its forces. Over time if a hive fleet can be prevented from feeding then it can be reduced to impotency due to a lack of biomass.