For insects, the Amazon’s canopy contains a dazzling multiverse

A new study finds that high in rainforest trees, insects live in ecosystems that vary wildly from the forest floor on up.

Published 2 Mar 2022, 17:51 GMT
Trapped at eight meters (26 feet) above the ground, this yet-to-be-named phorid fly species is a ...
Trapped at eight meters (26 feet) above the ground, this yet-to-be-named phorid fly species is a “parasitoid death-dealing machine” that jabs its eggs into other insects, says entomologist Brian Brown. Brown, the curator of entomology at the Natural History Museum of Los Angeles County, photographed the insects in this article using a camera-and-microscope setup that was originally developed to examine flaws in computer chips.
Photograph by Brian Brown, Natural History Museum of Los Angeles County

“I thought, my God, this is like someone’s discovered another continent!” says Brian Brown, an entomology curator at the Natural History Museum of Los Angeles County. He was talking about insects.

When studying insects in the Amazon, most entomologists cast their eyes down, to the intricate pathways of moss and underbrush that make up the rainforest floor. But José Albertino Rafael wanted to look up. Really far up—to more than 105 feet in the canopy. 

Two hours northwest of Manaus, Brazil, a 131-foot steel tower rises from a pristine area of the rainforest. Built in 1979, the tower had long been used to track the exchange of carbon dioxide between the trees and the atmosphere, but more recently it has been used for pioneering entomology research.
Photograph by Craig Cutler

During two weeks in 2017, Rafael, an entomologist at Brazil’s National Institute of Amazonian Research, and colleagues trapped insects at various heights, starting at ground level, from a 131-foot tower erected in the middle of the Amazon, just outside Manaus.

The findings were staggering, says Brown, who was part of a team that examined and recorded all 37,000 insects that were collected. Nearly half of them were flies. “There were weird and different things. I didn’t even know what genus these were, let alone species.”

Tumbling flower beetles have a triangular body that helps them escape predators.

Photograph by Brian Brown, Natural History Museum of Los Angeles County

The results of their analysis, published in Nature on February 2, point to a distinct and previously unexamined network of ecosystems in rainforest trees. More than 60 percent of the 857 species of flies collected, for example, were found above ground level. Many, if not most, likely are new species, Brown says.

Previous studies have compared insects on the ground with those in the canopy, but this is one of the first efforts to understand insect diversity at smaller vertical intervals.

The mantis wasp uses its ovipositor—a needlelike organ for laying eggs—to pierce the egg cases of mantises. When the wasp’s larvae hatch, they feed on the mantis’s eggs.
Photograph by Brian Brown, Natural History Museum of Los Angeles County

The findings underscore how much of the insect world still remains undiscovered, says Floyd Shockley, the collections manager of the entomology department at the Smithsonian Institution’s National Museum of Natural History, who was not involved in the study.

“Millions of things that live in the tropical canopy never come to ground,” he says, adding that these kinds of vertical studies “are incredibly important because [without them], we’re missing out on a tremendous amount of biodiversity.”

Sorting insects

To collect the insects, Rafael set five large, tent-like netted traps off the tower at 26-foot intervals, starting at ground level and reaching up to 105 feet.

Both the forest canopy and the undergrowth are patrolled by parasitoid wasps seeking their prey—mostly caterpillars.
Photograph by Brian Brown, Natural History Museum of Los Angeles County

Brown and Dalton de Souza Amorim, an entomologist at the University of Sao Paolo, and the rest of their team first sorted the insects by order (flies, beetles, bugs, and more). They focused on Diptera—flies—sorting more than 16,000 specimens into 56 families, then into 857 species. It’s unclear how many of those species are new to science. “It would take years and a ton of research to find out,” Brown says, but he guesses that many or most are undescribed.

Some families of flies were most abundant and diverse on the ground. Others were concentrated in the canopy. Still others peaked at the middle levels. Notably, between 90 and 100 percent of specimens of some families of flies were found in the four highest traps. 

The watchful jewel beetle's massive eyes allow it to flee from predators—and researchers—quickly, making the beetles difficult to collect for study.
Photograph by Brian Brown, Natural History Museum of Los Angeles County

What’s the bigger picture?

 So much remains unknown about insects. “We’re still finding fish and amphibians, but we’re getting pretty close on birds and mammals to having a complete picture on their diversity,” Shockley says. But scientific models estimate the number of undiscovered insect species at between five and 30 million. “Every time we get one of these studies, it helps us improve the model so we can see how much we haven’t discovered.”

There are many reasons why knowledge of so many insect species remains elusive. “They’re small, they’re fast, they’re highly diverse, and they can occupy almost any niche,” he says.

So “we have to understand how they interact with each other, us, and crops,” Shockley says. “And we can’t talk about what they’re doing until we put a name on what they are.”

Iridescent orchid bees, tropical cousins of bumblebees and honeybees, are among the multitude of insects that entomologists have collected at the observation tower.
Photograph by Brian Brown, Natural History Museum of Los Angeles County

Most insect sampling has been done based on latitude and longitude and sometimes altitude—up a mountain, for example, where habitats can change dramatically. But by collecting insects vertically in forest habitats, which is hard to do, Shockley says, “we’re adding an additional dimension to our understanding of diversity in three-dimensional space.”

Flies get a bad rap—it can be hard for people to understand why we should care about them. “But organisms [like insects] are arguably way more important than mammals or birds for the structure of the forest,” Brown says. “They’re important for pollination, energy, recycling, and more. What would happen if there were no insects feeding on decaying bodies? The ecosystem services they provide are so vital—but almost invisible.”

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