What you do is get a good warmer design, and get about 3-4 fleets.  For each attack on the reavers only get about 5-10k swarmers in each fleet, and attack.  All of the swarmers will die, but you will be able to do a lot of damage to the reavers.  Then buy 5-10k more i neach fleet and continue doing that until the reavers are dead

Swarm Mod Info
Ok I am going to try and start updating this again with anything I can think of to help new spaceo Players now I am going to Document how the Swarm Mod works.

The way the Swarm mod works is if you have lots of ship in one fleet you get a bonus to HP/ATT/Defense dependent on the ships size(Smaller gets a bigger bonus) and the Number of ships in a fleet.

The bonus caps out after a Specific number of ships dependent on the ships size. A smaller ship size needs more ships to max the Bonus .

Larger ships just cap out at lower ships numbers

For now here is the Data on the Bonus for ships size 62 and up since its the same mod after that.

Maxes Bonus at 8,000 Ships
Max Attack Bonus: 2.42857x Normal
Max Defense Bonus: 2.42857x Normal
Max HP Bonus: 11x Normal

Size 12 Ships
Maxes Bonus at 24,000 Ships
Max Attack Bonus: 5.285714285714285568x Normal
Max Defense Bonus: 5.285714285714285568x Normal
Max HP Bonus: 31x Normal