It is a safe bet that a "worm" as you describe in a ripe guava or any other ripe sweet fruit is a fruit fly.
![fruit fly larvae]( from <
Fruit flies are attracted to any ripe sweet fruit. They are also attracted to vinegar and alcohol - both produced by yeast in and on the fruit, which is the high protein food that the fruit flies are really after in the fruit.
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> When ripe, guavas emit a pungent, musky odor that attracts fruit flies. Fruit flies lay their eggs beneath the fruit's skin, and the maggots feed on the flesh. The damage causes guavas to rot. Fruit fly infestations often spread quickly, but prompt treatment can get populations under control.
The fly large actually speed the rotting of the fruit by moving yeast around on their bodies.