Insects are often called the foundation of terrestrial and freshwater food webs. With an estimated 5.5 million species and a combined biomass that dwarfs that of all terrestrial vertebrates combined, they occupy almost every trophic level — as herbivores, predators, parasitoids, and decomposers. Remove insects from any ecosystem and the consequences would be catastrophic.
Insects as Prey
Perhaps the most obvious role insects play in food chains is as a food source for a vast array of other animals. Their sheer abundance and nutritional value make them indispensable prey items.
| Predator Group | Insect Prey | Examples |
|---|---|---|
| Birds | Caterpillars, beetles, flies, aphids | Blue tits, swallows, spotted flycatchers |
| Bats | Moths, mosquitoes, beetles, caddisflies | Common pipistrelle, greater horseshoe bat |
| Freshwater fish | Mayfly nymphs, caddisfly larvae, midges | Trout, salmon, grayling |
| Amphibians | Flies, beetles, ants, woodlice | Common frog, smooth newt |
| Reptiles | Crickets, grasshoppers, beetles | Common lizard, slow worm |
| Other invertebrates | Aphids, caterpillars, fly larvae | Spiders, centipedes, predatory beetles |
The Blue Tit Example
A single pair of blue tits raising a brood of eight to ten chicks will collect an estimated 10,000 caterpillars during the nesting period. The timing of their breeding season is synchronised with the peak availability of moth caterpillars on oak trees. When this timing is disrupted — by climate change, for instance — chick survival rates plummet.
Did you know? A single common pipistrelle bat can consume up to 3,000 insects in a single night, including midges, mosquitoes, and small moths.
Insects as Predators
Many insects are themselves formidable predators, regulating the populations of other invertebrates. Ladybirds consume vast numbers of aphids. Dragonfly nymphs are apex predators in pond ecosystems. Parasitoid wasps lay their eggs inside the bodies of other insects, with the developing larvae consuming the host from within. These predatory and parasitoid insects provide natural pest control services worth billions of pounds annually.
Key Insect Predators and Their Prey
- Ladybirds: A single seven-spot ladybird can eat over 5,000 aphids in its lifetime
- Dragonfly nymphs: Prey on mosquito larvae, tadpoles, and even small fish
- Ground beetles: Consume slugs, caterpillars, and other soil invertebrates
- Lacewing larvae: Known as “aphid lions” for their voracious appetite for aphids
- Parasitoid wasps: Regulate populations of caterpillars, beetles, and flies
Insects as Decomposers
Decomposition — the breakdown of dead organic matter — is one of the most essential ecosystem processes, and insects are among its most important agents. Without decomposer insects, dead plant and animal material would accumulate, nutrient cycling would stall, and soils would become infertile.
Key decomposer insects include dung beetles, which bury and process animal faeces; carrion beetles and blowfly larvae, which break down dead animals; and bark beetles and woodboring beetle larvae, which decompose fallen timber. Termites, though not present in the UK, are among the most important decomposers of dead wood in tropical ecosystems.
Cascading Effects of Insect Decline
The well-documented global decline in insect populations — sometimes called the “insect apocalypse” — has cascading consequences throughout food webs. Declining insect abundance has been linked to:
- Bird population declines: Insectivorous bird species such as the spotted flycatcher and swift have declined by over 50% in the UK since the 1970s.
- Reduced pollination: Fewer pollinating insects means lower crop yields and reduced wild plant reproduction.
- Slower decomposition: Reduced decomposer populations slow nutrient cycling and organic matter breakdown.
- Fish population impacts: Declines in aquatic insect larvae reduce food availability for freshwater fish.
- Disrupted pest control: Fewer predatory insects allow pest species to proliferate, increasing reliance on chemical pesticides.
The Bottom-Up Foundation
Ecologists describe insects as the “bottom-up” foundation of most terrestrial food webs. They convert plant biomass into animal biomass that is then available to higher trophic levels. In essence, insects are the critical link between primary producers (plants) and the vertebrate world. Without this link, ecosystems as we know them could not function.
Key Takeaway
Insects are indispensable components of food chains, serving as prey for birds, bats, fish, and amphibians, as predators that control pest populations, and as decomposers that recycle nutrients. Their decline threatens the stability of entire ecosystems and the services they provide to humanity.