Hit Points of Giant Insect

Question

The description of Giant Insect says

You transform up to ten centipedes, three spiders, five wasps, or one scorpion within range into giant versions of their natural forms for the duration. A centipede becomes a giant centipede, a spider becomes a giant spider, a wasp becomes a giant wasp, and a scorpion becomes a giant scorpion.

Each creature obeys your verbal commands, and in combat, they act on your turn each round. The GM has the statistics for these creatures and resolves their actions and movement.

A creature remains in its giant size for the duration, until it drops to 0 hit points, or until you use an action to dismiss the effect on it.

The GM might allow you to choose different targets. For example, if you transform a bee, its giant version might have the same statistics as a giant wasp.

In Giant Insect lacks typical text, unlike other similar "transform" spells (e.g., Polymorph):

The target assumes the Hit Points of its new form. When it reverts to its normal form, the creature returns to the number of Hit Points it had before it transformed. If it reverts as a result of Dropping to 0 Hit Points, any excess damage carries over to its normal form.

In this case, do I understand correctly that for this transformation all these points are invalid? I'm confused by the beginning and ending of spell, because then Giant Scorpion gets Hit Poins of common Scorpion on start, and vice versa on end. Or this part of the text implied in "The GM has the statistics for these creatures..."?

UPD: For clarify, the biggest question here is stat's change is meant to replace actual HP and max HP, or only max HP. It seems to me that only max HP (And that's why Polymorph has such a text. If this text not there, then the form does not receive actual HP).

Answer 1

The insect assumes the stats of its giant version, and after dropping to \$0\$ HP returns to its original stats and HPs.

The description of the spell says (emphasis mine)

A centipede becomes a giant centipede, a spider becomes a giant spider, a wasp becomes a giant wasp, and a scorpion becomes a giant scorpion.

The GM has the statistics for these creatures\$^1\$

[...]

A creature remains in its giant size for the duration, until it drops to 0 hit points, or until you use an action to dismiss the effect on it.

Consider for the example the Scorpion, who has just 1 HP: if it is the target of Giant Insect then it is transformed in its giant version, having thus 52 HP (and also all the other characteristics described in the stats block).

It remains in the giant form until

• the spell ends: after 10 minutes or if caster's concentration is broken
• the caster voluntarily decides to dismiss the spell
• it drops to 0 HP

In the latter case, since the description does not present any ruling like the Polymorph spell, this means that the creature reverts to its original size with the HP that it had before begin targeted: this is given by reading

A creature remains in its giant size for the duration, until it drops to 0 hit points, or until you use an action to dismiss the effect on it.

as if one of the above conditions is satisfied then the creature remains in its giant size, otherwise it reverts in its original form.

Two examples are provided, in order to clarify the above ruling.

1. Consider again a scorpion with just 1 HP: it is targeted by Jaheira with the Giant Insect spell, it becomes a Giant Scorpion with 52\52 HP. After a couple of rounds against a pack of Gnolls, its HP drop down to 40\52, Jaheira looses concentration and then the beast reverts to its original form, a tiny scorpion with 1 HP.

2. Consider a spider with 3\3 HP\$^2\$: Bruenor the Dwarf tries to kill it, but the spider takes only 2 damage, having thus 1\3 HP. The spider is then the target of a Giant Spell cast by Arundel the Druid, it is transformed in a Giant Spider with 26\26 HP. Bruenor, after a couple of rounds, reduces the HPs of the Giant Spider to 0: then, the monster reverts in its original form, with 1\3 HPs, i.e. with the amount of HPs that it had before being targeted by Giant Spell.

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\$^1\$ The DM has access to the stats block of the giant version of these insects in the MM.

\$^2\$ A DM can decide to roll HPs also for monster: I usually do.

Answer 2

The hit points of the giant insects are whatever the Monster Manual says they are

Although its not obvious from the player's point of view, giant centipede, giant spider, giant wasp and giant scorpion are all specific "monsters" in the Monster Manual.

When it states that a spider becomes a giant spider, it is referring to the fact that a giant spider, as per the Monster Manual, will now appear in place of the original spider. This is evidenced by the fact that it says the DM will have the statistics for these creatures and, in DnD Beyond, the text actually links to the monster stats.

I understand it lacks the typical mention that other spells like Polymorph have that explains exactly how one set of statistics get replaced by another. But the difference here is that ordinary spiders, centipedes etc don't have statistics in the gaming sense of the word. Hence no such explanation is necessary. You had a spider. Now you have a giant spider.