From Exterminatus Manual
Tyranid Lictor (Lictor)
Lictors are the stealth and reconnaissance units of the hive fleet. They are the eyes, ears and sensory organs of the hive mind behind enemy lines. Solitary and silent their chameleon ability allows them to get into striking ranges of their talons.
Lictors are armed only with their Talons, chameleon ability and natural cunning. Primary attack lashes out with the talons, Secondary attack toggles the chameleon ability. With the chameleon ability in effect Lictors become transparent and nearly invisible. Lictors always turn off the chameleon effect before attacking or capturing an objective. Lictors can also perform a long leap by pressing the SPRINT and JUMP keys together. Using their leap Lictors can reach ambush spots and hide outs that would normally be unreachable.
Lictors are one of the only class in Exterminatus that doesn't have a gun, so you'll have to rely on your chameleon ability to stay hidden long enough to get in close and use your talons. A peculiarity of the lictors talons is that they have a greater striking distance when attacking upward. Having a nearly invisible enemy can be intense and scary, inducing paranoia and causing players to shoot at shadows. Nurture the fear. Beware that your hoof steps, although softer than other tyranids, can give you away in quiet areas. The lictor is easier to spot when in the open, try lurking close to walls, objects and shadows to become harder to detect. Running head on into the enemy is a sure fire way to get noticed; the art of using the lictor is to work your way behind their lines and to wait for an opertune moment to catch them unaware. Wounds also are not hidden by the chameleon effect, once you're wounded you become more vulnerable. Tarantulas can detect a Lictor even when cloaked, however you can usualy use your leap ability to get behind the turret and destroy it.