Fruit flies utilize alcohol in multiple ways. Pregnant females place their eggs in the alcohol of fermenting fruit to protect them from wasps, who can't tolerate alcohol. Alcohol can also serve as a life-saving measure during a wasp attack. Wasps often lay eggs inside fruit flies, and by consuming alcohol the fly is ensuring that any potential wasp eggs are eradicated from its body - thus saving his own life!
Additionally, male fruit flies who have been rejected by a female are more likely to consume alcohol than fruit fly males who mate successfully - a practice common in, ahem, other species as well.
2. Vervet monkeys