Aliens are AI ships, similar to Pirates, that attack any Ship/Starbase (except Mega Base) in sight. They can even attack Pirates.

They spawn in groups of 3-5 at random locations on the map and have an 8% chance of being an Alien Punisher.

If destroyed, they leave a wreck that contains loot, though it is much less than a player-made ship.

Occasionally, what some players call an "Alien Fleet" will spawn. This is pretty much a massive collection of alien ships, and they can be incredibly dangerous. Sizes of fleets have been seen to reach up to 300 in the past.

Thanks to a new update, the aliens can no longer do this, maxing out at 10 ships. If they're all Punishers, you're going to have a bad time.

Alien Swarmer

The Swarmer is a small alien frigate known for annoying miners. The Swarmer has 1 Light Turret, however, it is not the same as the Turrets on player owned ships, but sometimes it goes to harass freighters while attempting to go at the Mega Base.

It is colored green with a blue stripe.

It fires a neon green laser with high accuracy.

It is currently the most common alien spawn and is rather weak, although, in numbers, they are a force to be reckoned with.

These are best attacked with small ships with a good amount of light turrets, as Swarmers are small and fast, making them a hard target for larger turrets.

Swarmers have low health with only 300 hull and 300 shields but can still take a bit of a beating.

Swarmers drops only a small amount of loot.

Alien Punisher

The Punisher is an alien battleship which can pose a problem for weak starbases and any unfortunate player owned ships who are caught in its path.

It is covered in turrets similar to those of the Swarmer (five small alien lasers and five medium alien railguns), except they are much longer ranged, and the sheer amount of them can wreak havoc on whatever it targets.

It is colored green.

As of an update, Punishers have become very common, and sometimes you will find multiple Punishers in a single place. A player who owns a battleship (most likely a Hawklight, Warlock, or Ampharos) may be able to beat this monster alone with the help from a Starbase. Attack these with caution; use either a dreadnought or a fleet of battleships and/or battlecruisers. Skilled players have been able to solo them without base help with battleships. Some extremely skilled players can solo them with base help in a battlecruiser or cruiser.

The Punisher's weapons are extremely powerful.

The Punisher drops a little loot not more than 54 items.

Punishers do not spawn at Mega Base but sometimes go there to harass light ships.

In the recent update .58a, the Punisher AI received an update, in which it will now chase crippled ships with less than 30% health remaining.

The Alien Punisher has 5000 shields and 3500 hull with a top speed of 110.

Tiny Alien Laser 

Base Accuracy: 0.010000000000000000208

Beam Size: 1

Damage: 25

Range: 4500

Reload Time: 2.5

Speed Denominator: 7250

Medium Alien Railgun 

Base Accuracy: 0.0020000000000000000416

Beam Size: 6

Damage: 125

Range: 7500

Reload Time: 4.5

Speed Denominator: 5750

"Call" ability

Aliens have the ability to "call" other swarmers, or a punisher, to their location. This often happens when a lone swarmer is attacked. The other aliens on the map will begin to gather up and attack you. This can be scary when on a server fighting aliens alone if you are not prepared.

Punishers often use this ability before attacking a starbase. This can be seen observing the minimap, as many swarmers will congregate around the Punisher(s) before sieging the base in a combined fleet.

Planet Capturing

Alien can capture planets and assimilate them (very rare). Once aliens have assimilated a planet they will continue to spawn many aliens and will not leave the planet, defending it from re-capture. Unwary players may attack the planet only to see more than a dozen swarmers and 1 or 2 punishers attacking them.

Getting back the planet can be difficult, especially if the aliens manage to upgrade the planet, where in addition to aliens, turrets will pose a threat to players. A single dreadnought will not be enough to take back the planet if there are many aliens spawned there. Usually, 3 dreadnoughts and two sieges will be enough.

Once the planet is taken back, aliens will begin to "panic", scattering in different directions before returning to normal behaviour.