So, it's time to bring about giant insects! How? Gigantis! The one Enchantment that makes giant animals possible! Why? Because giant spiders and their ilk are a fantasy staple, and besides why not?!
The question, is How Can Insects Gain Gigantis?
The ways to gain Enchantments are as follows:
Use Natural Weaponry One way to get an Enchantment is to use one's own body (or parts of one's body) to kill the monster with the desired Enchantment. No, injuring it won't do, the magic will escape the killed cells and return to the still-living soul.
Lucky Sacrifice Another way to get an Enchantment is to be alive inside the monster with the desired Enchantment when it is killed. This would require an insect to get eaten by the Giganto, not to mention exposure to the Giganto's saliva or stomach acid (as this method is the inverse of "you are what you eat," AKA "you are what eats you").
Eating Eating part of the Giganto will grant a portion of its Enchantment to the consumer, especially if the flesh is fresh (read: still alive). However, this is a very inefficient method, as the Enchantment received is directly proportional to 1) how much you ate of the monster subtracted by 2) how much you actually digested the monster flesh.
Any insect using this method would have to gain the full Enchantment, eating an entire Giganto's worth of flesh or more (likely more) to succeed. Luckily, Dropped meat doesn't lose potency, so flies have a decent shot at succeeding, as long as they can gain Gigantis within a single fly's lifespan and then reproduce.
- Mimicry Plenty of insects eat bushes, so why not Leafmaw? That should allow insects to gain their giant size from Engulfers, when otherwise Engorgement would result in a gigantic corpse (ah, death by supersizing. Square-cube law, did you have to?).
Specifications for Best Answer:
The best answer will take each method and evaluate it to determine which would succeed and why.
The best answer will also determine which bugs will succeed using this method. Specific species aren't necessary; if you tell me flies will succeed and explain your reasoning, that will suffice. If you want help, feel free to search my various Gaining Enchantment questions to aid you. No, I can't answer this question myself, otherwise I wouldn't be asking! I'm no entomologist!