It's the end of the world as we know it ... (well, maybe)
Spiders have a very important role in the ecosystem. On average, each spider eats almost 2,000 insects a year. This greatly reduces the population of flies, but that doesn't give up hope for the fly population. Flies continue to make many babies so that more will survive to create more babies. Spiders basically control the population of flies, depending on how many they eat. If, all of a sudden, spiders no longer existed on Earth, the fly population would be extremely high. These flies would swarm the world, destroying all crops, therefore cutting off the food supply, and maybe even killing people as they go. Without spiders, the world could come to an end, whether it be by too many mosquito bites, or starvation. The video below goes more into detail about what would happen if all the spiders disappeared.