ok so here are some tips if you do not want the flesh taking over your world ;)
1 set the difficulty to peaceful (defeats the point but ok)
2 they are scared of fire and are very weak to it so make sure you have a flame bow, fire aspect sword or flint and steel
3 to signal that a hive spawned you will hear a schreech it will spawn something like 200 blocks from your position
4 make sure before you first kill the hive and then clear the biome for this use clay bombs, a flint and steen or lava buckets
5 the hive can make tissue much slower in colder biomes in addition to its weakness for fire
6 play it with friends :D its way more fun and they can help you defeat it
here is a challenge for ya let the hive sit for the first 10 days
and then look if you can defeat it