Harridan
Harridans are one type of the fuck huge Tyranid Bio-Titans. Harridans however, are fuck huge Bio-Titans with wings. Because they're mostly airborne their legs have been reduced to stumps, and for some reason the moment they land is like a death sentence since they cannot take-off again... Yes, despite having EXBOXHUGE Wings they still have the same weakness as ordinary boring albatross birds. Whether this is an absurd Derp that the Hive Mind greatly needs to fix, or whether this is just maximum efficiency (most Harridans don't hit the ground until they're already dead) is up for debate.
Being a living creature and relying upon wings rather than jet engines, the Harridan cannot match an aircraft for straight line speed, but its lithe, twisting body is far more maneuverable, allowing it to twist and turn to avoid enemy fighters or ground fire. A Harridan lacks the speed to dogfight effectively with Imperial flyers, although Imperial pilots' after action reports tell tales of Harridans intercepting aircraft that fly too close, or of them sacrificing themselves in suicidal mid-air collisions that destroys both the aircraft and the Harridan which is both unproductive for either races and awesome at the same time. Although in all honesty a creature this size should NOT be able to twist its body or at the very least be very maneuverable as what the fluff states. I mean the primary reason why flying animals gets big is for them to travel extremely long distances via sacrificing either speed or maneuverability. Is this a case of Tyranids giving evolution the middle finger or another case of GeeDub's basic failure of simple biology? You decide.
Harridans seem to act as brood mothers to smaller Gargoyles. A brood of as many as 20 Gargoyles can cling to the belly of the Harridan who acts as a “carrier” of sorts to transport the smaller Tyranid flyers, who, according to many experts, are incapable of long-distance flight. With a Gargoyle brood attached a Harridan's belly appears to constantly writhe with hideous clusters of scaly limbs and leather wings, writhing over the mother's skin and chitinous armour plates. As the Harridan soars over the battlefield the Gargoyles will detach themselves and flap off to attack the enemy. When Harridan's gather for a large attack, swarms of Gargoyles will usually darken the skies around them.
Tl;dr, they're basically a fucking insect dragon IN SPHESS!