Insects Do More for Vertebrates Than Provide Food, Review Finds

Nearly three-quarters of terrestrial and freshwater vertebrates eat invertebrates, and insects frequently make up a large share of their diets. But the study, led by Eliza Grames, an assistant professor of biological sciences at Binghamton University, State University of New York, describes relationships that go well beyond predator and prey, spanning an estimated 14m to 30m insect species worldwide.

Chimpanzees have been recorded applying insects to treat open wounds, and more than 200 bird species use ants to remove parasites or maintain their feathers. Some birds build nests near wasps or other stinging insects, apparently to gain protection from predators.

Insects also supply shelter. Birds, reptiles and mammals use termite mounds and ant nests, which can offer stable temperatures and humidity, and white-throated round-eared bats excavate cavities in termite mounds and use them as roosts.

Others act as sanitation workers. Dung beetles remove animal waste and can make dung drier and more aerated, reducing parasite survival, while moths living in some bird nests consume feces, feathers and other debris. The review cites evidence of beetles feeding on feathers in dinosaur nests during the Cretaceous period, which lasted from about 145m to 66m years ago, as a sign that such functions have operated for millions of years.

Other documented relationships include beetles removing ectoparasites from rodents, snakes feeding on firefly larvae to obtain defensive toxins, and antbirds using live crickets during courtship. Some are mutually beneficial: sloths rely on moths to deposit nitrogen in their fur, spurring algal growth that the sloths eat, and descend from trees about once a month to defecate on the ground, providing substrate in which moths lay eggs.

The review says the "widespread and considerable disruption" of insect communities is "inevitable" as land use changes, although the extent of declines varies across habitats and regions. Grames called the findings a "wake-up call for anyone concerned about the biodiversity crisis" and said insect conservation should be a top priority. "Insects are so much more than just food for vertebrates like birds and bats – they create and maintain habitat, provide protection to other species, help with reducing diseases and removing waste, and so many other ecosystem services that we, and other species, rely on," she said. "They really are the unsung heroes of the natural world."

Grames also pointed to the role insects play in the carbon cycle, saying about 12% of the global carbon forest stock is leaf litter and dead wood and that insects decompose about 30% of it. She said insects help forest regeneration by dispersing seeds into areas where larger seed dispersers have disappeared, and that pollination and seed dispersal, both carried out by insects, are two of the biggest limitations on forest regeneration.

The study says the lack of systematic descriptions of trophic and non-trophic interactions, hampered by an ongoing decline in natural history research, makes it difficult to understand how changes in insect biodiversity affect other species. Chris Elphick, a co-author and a professor of ecology and evolutionary biology at the University of Connecticut, said understanding the diverse roles insects play in vertebrates' lives is essential for designing effective conservation strategies. "If you want to have vertebrates, then you've got to be thinking about insect conservation, and we don't do that nearly enough," he said.