Dretch

The dretch is the smallest alien. The dretch attacks automatically when you are close enough to an enemy human.

=Techniques=

Don't get in the way
If there are bigger aliens around, you don't want to be underfoot. Stay out of their way so you don't block them by keeping to the sides and on the walls or ceiling.

Go for the easy prey
Take a look at the human you are attacking. If they are wearing a helmet they will be much harder to kill, and dretches hardly do any damage to humans in battlesuits. Avoid humans with helmets or battlesuits and wait for easier prey. Or wait for a bigger alien to attack and help take them out with a final bite to the head.

Ambush your prey
Climb a wall near an entrance and wait for a human to come all the way out. This is much easier than chasing after them, or running into their base only to be killed by their turrets.

Don't run straight at a human
If you run straight at a human, they will gun you down quickly, because they can easily set up a line of fire and take you out before you know what hit you. Try to attack them from the sides.

Headbite
When you are attacking with the dretch, always aim (look) at the head of an enemy human to bite him in the head. This takes off 96 hp (hit points). If you are looking only at their legs, you take off much less, so always aim for their head if you can.

Wallbite
In narrow areas, like hallways, don't attack from the floor. Instead, climb up and run along the wall while looking at your target. Bite the human right on top of the head where it's hard for them to see you.

Super jump
Climb up a wall and as you reach the top, turn off wallwalk. You will fly up into the air, and you might even be able to take out an annoying human with a jetpack.

Killing turrets with dretch
If you see a single turret one dretch can take it out! Check which way the turret is pointing, and approach it from the side. Run up to it and bite it while circling around it. The turret can't turn fast enough to get you. If there are multiple turrets you'll get shot in no time, so only try this with single turrets. This should only be attempted if there are no humans nearby, since running around a turret makes you an extremely viable target.