Quick Answer
An insect-free world would face an enormous ecological crisis. Many birds, amphibians, reptiles and mammals would lose prey, many plants would lose important pollinators, and decomposition and nutrient cycling would change. Humans could still grow wind-pollinated staple crops, but ecosystems and agriculture would be radically altered.
Insects occupy an enormous range of ecological roles. They pollinate plants, consume vegetation, recycle organic matter and serve as food for other animals.
Food webs collapse in places
Many insect-eating animals would lose a major food source. Some could switch to other prey, but specialists would be much more vulnerable.
Pollination falls
Some plants rely on wind or self-pollination, while others depend heavily on insects. Fruit and seed production would therefore decline unevenly rather than uniformly.
Decomposition changes
Insects such as beetles, flies and termites help break down dead organisms and organic material. Microbes would continue decomposing matter, but the pace and pathways would change.
Agriculture adapts unevenly
Staple grains would remain possible because many are wind-pollinated, but fruits, nuts and many vegetables would become harder to produce at current scales.
Established scienceNot all pollination is done by insects, and not all decomposition depends on insects. The effects would therefore be severe but not identical across ecosystems.
The bottom line
An insect-free planet would still have plants, microbes and vertebrates, but one of the most important ecological layers would be missing. Food webs and nutrient cycles would be transformed.
A note on our approach: Every article on WhatIfLab separates what current science establishes from what remains genuinely speculative. Where we cite a figure or finding, it reflects published, mainstream research at the time of writing — not a prediction dressed up as fact.