The Mantis began suffering damage almost immediately after the temperature descended beyond a critical point.
The cold started penetrating its natural defenses faster than its body could compensate. Not instant damage but progressive deterioration that accumulated with each passing second.
The cold penetrated from all directions simultaneously in a manner that made defending effectively against the practically environmental assault impossible.
Externally, the frigid air attacked its exoskeleton, which could resist physical impacts and ordinary elemental attacks but didn't have perfect protection against extreme temperatures. Chitin was excellent armor against cutting and crushing forces. Less excellent against thermal stress. The material became brittle at low temperatures, with microscopic fractures forming as the molecular structure lost flexibility.
