The Fly on the ceiling, it is true, occupies the same attitude; but she has her moments of rest: she flies, she walks in a normal posture, she spreads herself flat in the sun.

Besides, her acrobatic feats do not cover a long period.

The Empusa, on the other hand, maintains her curious equilibrium for ten months on end, without a break.

Hanging from the trellis-work, back downwards, she hunts, eats, digests, dozes, casts her skin, undergoes her transformation, mates, lays her eggs and dies.

She clambered up there when she was still quite young; she falls down, full of days, a corpse.
Things do not happen exactly like this under natural conditions.