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).