An international review, with the participation of a researcher from Miguel and the University of Haifa, points to diverse connections between insects and vertebrates — and warns of harm to them due to the decline in insect populations
Chimpanzees place insects on wounds, birds use ants to groom themselves, and reptiles lay eggs in termite mounds. Insects play roles in animal life that go far beyond providing food. An international review published September 30 in Nature Reviews Biodiversity summarizes the evidence for these connections and the risks associated with changes in insect diversity and abundance.
The review was led by Rob Cooke of the UK Centre for Ecology & Hydrology, Eliza Grames of Binghamton University, and Chris Elphick of the University of Connecticut. Among the authors is Yuval Cohen, whose affiliations in the paper are the MIGAL Research Institute and the University of Haifa.
The team examined nearly 300 studies conducted over about 75 years on terrestrial and freshwater vertebrates: mammals, birds, reptiles, amphibians, and fish. This is a review of existing literature, not a single experiment that demonstrated a uniform effect across species.
Not just a meal
Insects and other invertebrates are an important food source. Almost three-quarters of the vertebrate species for which data were available eat invertebrates, and more than two-fifths feed exclusively on them. The data refer to the species studied and for which data were available, and not to a count of all vertebrates in the world.
The dependence can also be indirect: plant foods are available through pollination and seed dispersal. Animals also consume insect products, including honey, wax, and honeydew. Some birds use insect silk and spider webs to build nests.
Homes, cleaning and chemical protection
Termite mounds and ant nests provide other animals with hiding places, breeding sites, and suitable humidity or temperature conditions. Birds may place nests near stinging insects, making it difficult for predators to approach.
The partnerships can also be surprising. Moths living in the fur of sloths may contribute nitrogen that encourages algae growth. Moths in the nests of owls and kingfishers break down leftover fur, feathers, and droppings. In doing so, they participate in the removal of waste from the nest.
Dendrobaterian frogs accumulate toxins from ants and beetles that they eat and use for defense. Insects can also reduce disease risks by decomposing dung or eating harmful insect larvae. In contrast, the use of insects on wounds by chimpanzees is an observed behavior; this alone does not indicate proven medical efficacy.
Both damage and knowledge gaps
Not every relationship is beneficial. Some insects prey on small vertebrates, while others transmit pathogens. Dragonfly larvae can eat tadpoles and small fish, and mosquitoes transmit diseases to birds. So changing the composition of insect populations can also change the balance of benefits and harms.
The authors emphasize that knowledge about non-nutritive relationships is fragmented, and common methods for comparing their importance are sometimes lacking. There are also biases between animal groups and regions of the world, and too few robust tests of causality between insect declines and changes in vertebrate populations.
Despite the limitations, the multitude of connections suggests that widespread insect declines may affect animals through several pathways simultaneously. The conclusion of conservation is that we also need to examine the ecological infrastructure on which the species we want to protect rely: food, shelter, reproduction, and interactions with other species.
Questions and Answers
Is the importance of insects limited to pollination and food?
No. The review also describes shelter, waste removal, protection from predators, and the use of chemicals.
Are all insects beneficial to all animals?
No. Some also prey on small vertebrates or transmit pathogens.
What is still missing from the research?
Systematic monitoring and causal testing will allow us to measure how changes in insects affect vertebrates, beyond reducing their food.
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