A scientific review of insect numbers suggests that 40% of species worldwide are experiencing "dramatic rates of decline".
The study indicates that bees, ants and bugs disappear eight times faster than mammals, birds or reptiles.
But researchers say that some species, such as houseflies and cockroaches, are probably booming.
The general decline of insects is caused by intensive agriculture, pesticides and climate change.
Insects make up the majority of the living creatures and offer significant benefits to many other species, including humans.
They feed birds, bats and small mammals; They pollinate around 75% of the world's crops. They complement the soil and keep the number of pests under control.
Many other studies in recent years have shown that individual species of insects, such as bees, have suffered major declines, especially in industrialized countries.
This new paper, however, looks wider.
The book, published in the journal Biological Conservation, examines 73 studies published all over the world published in the last 1
The researchers found that declines in almost all regions can lead to extinction of 40% of insects over the next few decades. One third of the insect species is classified as endangered.
"The main factor is the loss of habitat due to agricultural practices, urbanization and deforestation," said lead author Dr. Francisco Sánchez-Bayo from the University of Sydney told BBC News.
"Secondly, the world's increasing use of fertilizers and pesticides in agriculture and contamination with chemical pollutants of all kinds. Third, we have biological factors such as invasive species and pathogens, and fourth, we have climate change, especially in tropical areas areas, which are known to have a major impact. "
The highlights of the study include the recent, rapid decline in flying insects in Germany and the massive decline in tropical forests in Puerto Rico, which is associated with rising global temperatures.
Other experts say the results are "sobering".
"It's not just about bees or even about pollination and feeding ourselves. The downsides also include dung beetles that recycle wastes and insects like dragonflies that start life in rivers and ponds," said Matt Shardlow British activists Buglife.
"It is becoming increasingly apparent that the ecology of our planet is breaking, and intensive and global efforts are needed to stop and reverse these terrible trends, and continuing the slow eradication of insect life is not a sensible option."  Pests on the rise
The authors are concerned about the effects of insect decline along the food chain. Since many species of birds, reptiles and fish are their main food source depending on insects, these species are likely to be extinguished as a result. Image Caption
Although some of our major insect species are in retreat, the report also notes that a small number of species are likely to adapt to changing conditions and perform well.
"Fast-growing pest insects are likely to thrive on warmer conditions, as many of their natural enemies, which breed more slowly, will disappear," said Professor Dave Goulson of the University of Sussex, who was not involved in the review.
"It is quite plausible that we may fight only a few insect pests, but we will lose all the wonderful insects we want, such as bees and hoverflies, as well as butterflies and dung beetles that have a great job of eliminating animal waste . "
Prof. Goulson said some robust, adaptable, generalist species – such as houseflies and cockroaches – seem to be able to live comfortably in a man-made environment, and have developed resistance to pesticides.
He added that although the overall message was alarming, there were things that people could do, such as: To make their gardens more insect friendly, to use no pesticides and to buy organic food.
Further research is urgently needed, as 99% of the evidence for the decline in insects come from Europe and North America and almost nothing from Africa or South America.
When a huge number of insects have disappeared, they will eventually be replaced, but it will take a long time.
"If you look at what has happened in the great extinctions of the past, they have produced massive adaptive radiations" The few species that have managed to adapt and occupy all available niches and evolve into new species ", said Goulson to BBC News.
"Give it a million years, and I do not doubt that there will be a whole new set of creatures that have replaced those that were wiped out in the 20th and 21st centuries.
"Not much consolation I'm afraid for our children."