You're talking about Cicadas? Those live underground for 15-17 years feeding on sap from tree roots. But cicadas live more than 36 hours as adults. Most live several months during the summer, feeding on tree sap. They also, given their small size, have the greatest "sound to weight ratio" of any animal. If a cicada where the size of a human, they could (at least thoeretically) produce a sound louder than a jet engine.
However, if you want strange life cycles, you need to start studying parasites. For example, the ant fungus that causes it's host to climb up the tallest object it can find, and then clamp down with it's legs and mandibles. The fungus then paralyzes and finally devours it's ant host and uses the corpse to grow a tiny spore capsule.
Then there's a species of parasitic fly that infects male crickets. It finds the cricket by homing in on it's song. The fly then lays an egg on the cricket, and the larva feeds on the fat and body fluids. It finally grows so large that it completely devours the internal organs, and bursts out, killing it's host. (Rather like the movie "Aliens"; now you know where they got the idea.)
Then there are the so called "Horsehair Worms." these start as microscopic larvae swimming around in a source of water. When one of a number of insects drinks the water, it may pick up one of these larvae. It then slowly grows to adulthood inside the insect, and once it has, suddenly causes the insect to becone thirsty. Once the insect reaches water, the worm triggers a panic response; the insect runs, leaps, or crawls into the water and drowns. The worm then crawls out of the insect and bursts, releasing millions of tiny eggs.
It seems like, for every species of insect or small animal, there is a parasite that has figured out a particularly gruesome way of killing it. these are only three examples, there are hundreds of thousands of others. this is not limited to land animals either. ever heard of "whirling disease"
If you think things like that don't affect humans, think again. Firstly there is the parasite that causes malaria, "Plasmodium", whose life cycle is far too complicated to even outline here. Then there is the Ebola virus, which, like the Black Plague causes the intestines and respritory tract to leak blood, killing it's host and helping to spread itself. Then there are the many dozens of other human diseases caused by parasites,like Sleeping Sickness, Tapeworms, Schizstosomiasis, River Blindness, etc. And humans are just one species. Imagine how many other parasites are out there that infect other types of animals.
Now you said earlier that life seemed pointless. There is in fact a point to all this, it is Survival. Parasites may seem strange, but they have simply found a niche, and are exploiting it to the best of their ability in order to survive and reproduce. Don't go around accusing life of being wierd; you probably don't know the half of it!