The number of flying insects has declined by three-quarters over the past 25 years, according to a new study.
The data, which has shocked scientists, was gathered in nature reserves across Germany - but researchers say will affect all landscapes dominated by agriculture.
Discussing the new findings, scientists warned that the world is 'on course for ecological Armageddon', with dramatic impacts on society.
Although the cause of the plunge is unclear, experts believe the destruction of wild areas and excessive use of pesticides may have contributed.
Hans de Kroon at Radboud University in the Netherlands led the research.
He told The Guardian about the alarming new data: "The fact that the number of flying insects is decreasing at such a high rate in such a large area is an alarming discovery."
"Insects make up about two-thirds of all life on Earth [but] there has been some kind of horrific decline," added Prof. Dave Goulson of Sussex University, UK, and part of the research team.
"We appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological Armageddon.
"If we lose the insects, then everything is going to collapse."
For the study, entomologists in Germany began collecting insects in 1989,using special tents called malaise traps for capturing more than 1,500 samples of all flying insects at 63 different nature reserves across the country.
The researchers then measured the total weight of the insects in each sample - and discovered that the annual average plunged by 76 percent over the 27 year period, with the decline being even higher (82 percent) in summer - when usually, the insect numbers reach their peak.
The fact that the samples were taken in protected areas makes the findings even more worrying, said Caspar Hallmann at Radboud University, also part of the research team.
"All these areas are protected and most of them are well-managed nature reserves.
"Yet, this dramatic decline has occurred."
Lynn Dicks at the University of East Anglia, UK, explained why flying insects are essential for the environment.
"Flying insects have really important ecological functions, for which their numbers matter a lot," she says.
"They pollinate flowers: flies, moths and butterflies are as important as bees for many flowering plants, including some crops. They provide food for many animals – birds, bats, some mammals, fish, reptiles and amphibians.
"Flies, beetles and wasps are also predators and decomposers, controlling pests and cleaning up the place generally."
Discussing the cause of the decline, De Kroon adds: "We need to do less of the things that we know have a negative impact, such as the use of pesticides and the disappearance of farmland borders full of flowers."