The underestimated power of insects for life on earth

Many animals like to eat insects - but just thinking about that falls far short when it comes to the immense importance of insects for life on earth.

A team of more than 20 scientists has compiled many and little-known examples. For example, few people probably know that nectar-sucking hummingbirds, like massive grizzlies, sometimes owe their survival to small insects.

Nearly three-quarters of all terrestrial and freshwater vertebrates with available data eat invertebrates, with insects often making up the majority of their diet, according to the journal Nature Reviews Biodiversity. More than two fifths even do this exclusively.

The number of insect species on earth is estimated at around 14 to 30 million, explains the team led by Rob Cooke from the Center for Ecology and Hydrology in Wallingford. Public debates about the decline of insects often focus on their role as bird food. In fact, of the 580 bird species taken into account for the evaluation, around two thirds eat insects. These often make up more than half of the food.

But often it's not about the quantity, but rather about the timing: Many reptiles eat insects as young animals, including species whose adults mainly eat plants. For many birds, the supply and therefore the survival of the chicks depends on insects. Contrary to popular belief, even the delicate hummingbirds do not just sip nectar. Like other nectar or sap eaters, they need protein for growth and tissue development - and they grab insects to do this.

In midsummer, a period of intensive feeding before hibernation, grizzly bears can scavenge thousands of armyworm moths from under stones every day. The fat-rich insects ensure survival, especially in winter, when other prey species such as salmon are rare. Chimpanzees eat Macrotermes termites after wildfires when other food is scarce.

And some people can't get enough: the spadefoot toad Scaphiopus couchii can devour a quantity of termites equivalent to more than half its body weight in one meal. The study calls this enough to meet their calorie needs for a year. In the case of the mountain pygmy marsupial, also known as the mountain pygmy marsupial, reproduction depends heavily on the appearance of a single insect: the bogong moth. If things are bad for this spring food, there are hardly any offspring among the mouse-like marsupials.

There are also countless indirect connections: Some herons throw insects onto the surface of the water to attract fish. Insects pollinate plants and disperse seeds, which then provide food for vertebrates. Fig wasps, for example, pollinate fig trees - which benefit more than 1,000 fig-eating bird and mammal species, as Cooke's team writes.

There are also cycles of mutual benefit: moths live in the fur of sloths, for example. They introduce nitrogen, which causes the algae in the fur to sprout more. The sloth in turn munches on it. And when the need arises, the moths lay eggs in its feces, from which the next sloth inhabitants hatch.

Personal hygiene and infection protection

Insects not only provide other animals with food, but also with shelter and building materials. Numerous vertebrates use ant or termite burrows as breeding and retreat places. Some bird species also specifically build their nests near wasps or ants - presumably because their defensive neighbors deter nest robbers.

Ant grooming has been documented in more than 200 bird species, as the study states: Either a bird actively rubs individual ants into its feathers - or it sits on an ant trail or an anthill and lets the animals scurry into its feathers. It is assumed that the ant secretions inhibit feather parasites, bacteria or fungi.

Chimpanzees also rub insects on open wounds, which is interpreted as a possible case of self-medication. It is assumed that body substances from the insects used could have a pain-relieving, anti-inflammatory or antimicrobial effect. There is no reliable information yet.

Worms and protozoa

There are often indirect effects: Dung beetles and other dung-eating insects remove feces, which can contain pathogens and parasites. In some bird nests there are moths that break down droppings, feathers, fur or debris - and thus eliminate sources for the reproduction of parasites, for example.

But insects are not always “the good guys”. Avian malaria transmitted by mosquitoes affects bird species worldwide, the study says. Biting midges transmit the bluetongue virus among ruminants. Many pathogens that affect humans are also transmitted by mosquitoes. Fleas, in turn, transmit bacterial pathogens such as Yersinia pestis, the pathogen that causes plague.

And this is often forgotten: Insects are not only hunted, but also hunters: many of them prey on vertebrates, as the study states. Mantises catch hummingbirds; Aquatic insects such as dragonfly larvae, water bugs or water beetles prey on small fish and tadpoles.

Insects provide food, create nesting sites and shelter, help with hygiene and parasite control, and modify habitats. The nearly ubiquitous interactions between insects and vertebrates, the scientists say, clearly indicate that widespread insect declines are likely to seriously affect many vertebrate populations.

For example, there are clear connections between available insect prey and the reproductive success of birds. Around three billion birds have been lost in North America since 1970. The decline particularly affected species that rely on insects for at least part of their life cycle.