For many vertebrates, insects are more than a food source. As “little things that run the world”, insects provide critical functions such as protection, sanitation and shelter across ecosystems, according to a new study.
The study, published in Nature Reviews Biodiversity on Wednesday, sheds light on the various ways insects support vertebrates, ranging from birds and bats to reptiles, amphibians and mammals.
Nearly three-quarters of terrestrial and freshwater vertebrates eat invertebrates, according to the paper, with insects frequently making up a large portion of their diets.
However, their relationship goes beyond predator and prey.
The paper, led by Eliza Grames, an assistant professor of biological sciences at Binghamton University, State University of New York, documents dozens of less obvious ways vertebrates depend on the estimated 14m to 30m species of insects found around the world.
Chimpanzees, for example, have been recorded applying insects to treat open wounds, while more than 200 bird species use ants to remove parasites or maintain feathers. Other birds build nests near wasps or other stinging insects, in a likely effort to gain protection from predators.
Insects also provide shelter, the study notes. Birds, reptiles and mammals use termite mounds and ant nests, which can offer stable temperatures and humidity. White-throated round-eared bats, for instance, excavate cavities in termite mounds and use them as roosts.
Other insects act as sanitation workers. Dung beetles remove animal waste and can make dung drier and more aerated, in turn reducing parasite survival, according to the study. Meanwhile, moths living in some bird nests consume feces, feathers and other debris. The review notes that insects have performed similar functions for millions of years, citing evidence of beetles feeding on feathers in dinosaur nests during the Cretaceous period, which lasted from about 145m to 66m years ago.
Other insect-vertebrate relationships include beetles removing ectoparasites from rodents and snakes feeding on firefly larvae to obtain defensive toxins, as well as antbirds using live crickets during courtship.
Mutually beneficial relationships also occur across the insect-vertebrate realm, with sloths relying on moths to deposit nitrogen in their fur and spur algal growth, which the sloths then eat. Sloths then descend from trees once a month to defecate on the ground, providing substrate in which moths lay eggs.
According to the study, such overlooked relationships could become increasingly important as insect communities evolve. Although the extent of insect declines varies across habitats and regions, the review says that “widespread and considerable disruption” of insect communities is “inevitable” as land use changes.
Grames called the study a “wake-up call for anyone concerned about the biodiversity crisis”.
“We need to pay attention to insects and make their conservation a top priority, because conserving insects will benefit all the other species that rely on them. 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. They really are the unsung heroes of the natural world,” she added.
Grames also pointed to the critical role insects play in addressing the climate crisis, saying: “About 12% of the global carbon forest stock is leaf litter and dead wood, and insects are responsible for decomposing about 30% of it. So even though insects are small, their activities influence global carbon cycles. Insects also help with forest regeneration by dispersing seeds into areas where other, large – seed dispersers have disappeared. Pollination and seed dispersal, both of which are done by insects, are two of the biggest limitations in forest regeneration.”
Similarly, Rob Cooke, senior ecologist at the UK Centre for Ecology and Hydrology and a co-author of the study, highlighted the broader ecological implications of insect declines, saying: “Widespread insect declines globally are likely to have far-reaching effects on wildlife. Beyond reducing an essential food source, losses of insects risk changing ecosystems, disrupting pollination and seed dispersal, weakening sanitation, and altering the many interactions that help ecosystems function.”
The consequences for vertebrates remain difficult to predict due to the lack of studies on insect-vertebrate relationships. The study notes that “the lack of systematic descriptions of trophic and non-trophic interactions, hampered by an ongoing decline of natural history research”, makes it difficult to understand how changes in insect biodiversity affect other species.
For co-author Chris Elphick, a professor of ecology and evolutionary biology at the University of Connecticut, understanding the diverse roles that insects play across 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,” Elphick said.
