Nemesis: Retaliation · Board game rules
When does Larva trigger Shooting or Fire?
Quick answer
A Larva dies from just 1 Hit, whether from Shooting, Bursting, Melee, or Fire — no die roll is needed to confirm the kill, unlike other Intruders.
Details
Larva Health works differently from Adults and Drones: "In a Corridor 1 Hit is enough to kill a Larva. In a Room 1 Hit is also enough to kill a Larva - regardless of the number rolled on a Shoot die." [p.34 — Health of Other Intruders]. This means that when Shooting a Larva, you still make the Shoot roll as normal, but the result of that roll doesn't matter — a single Hit always kills it.
Fire also deals 1 Hit to any Intruder in a Room with Fire during the Intruder Burning step, but this Hit is dealt without rolling any die: "Since no die is rolled, this Hit can never kill an Intruder (except for a Larva)" [p.14 — Intruder Phase]. Because a Larva always dies from just 1 Hit regardless of any roll, Fire is capable of killing a Larva even though it normally cannot kill tougher Intruders.
Watch out: This special 1-Hit-kill rule applies only to Larvae. Adults and Drones need a successful die roll (Shoot/Melee) or specific Hit thresholds (2 Hits for Drones in Corridors) to die, so Fire alone (which deals a Hit without a roll) will never kill them — only Larvae are vulnerable to this "free" Hit from Fire [p.14 — Intruder Phase; p.34 — Health of Other Intruders].