Caddis fly larvae are now building microplastic shelters

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Roland Birke | fake pictures

Crawling along the bottoms of the world's rivers, caddis fly larvae experience a perpetual housing crisis. To protect themselves from predators, they collect grains of sand and other sediment and glue them together with silk, forming a cone that supports their worm-shaped bodies. As they mature and lengthen, they have to continually add material to the case; Think of it like adding rooms to your home for the rest of your life, or at least until you become an adult insect. If the caddis flies larva somehow loses its case, it has to start from scratch, and that's a pretty precarious situation for a defenseless meat tube. And now, the microplastic threat is piling up on the caddis fly tribulation list.

Microplastic particles [pieces of plastic less than 5 millimeters long] have already corrupted many of Earth's environments, including virgin and arctic deep-sea sediments. In a study published last year, researchers in Germany reported finding microplastic particles in cases of caddis flies in the wild. Then, last month, they published troubling results from lab experiments that found that the more microplastic particles a caddis fly larva incorporates into its box, the weaker that structure becomes. That could open caddis flies to further predation, sending ripple effects through river ecosystems.

Some examples of cases of caddis flies. Image A was collected from nature, and B was constructed of sand by a larva in the laboratory. In image C, the larva has incorporated black PVC particles. And in D, they are blue PET particles. "Src =" https://cdn.arstechnica.net/wp-content/uploads/2020/05/caddis-1.jpg "width =" 914 "height =" 704

Some examples of cases of caddis flies. Image A was collected from nature, and B was constructed of sand by a larva in the laboratory. In image C, the larva has incorporated black PVC particles. And in D, they are blue PET particles.

Tamara Al Najjar

You wonder why a species of insect matters. But caddis flies are critical actors in these ecosystems, and their struggles could have consequences. Caddis fly larvae are an important concert that sucks up aquatic vegetation, preventing a river from overgrowing. As flying adults, they serve as a critical food source for bats, frogs, and spiders. This study is also helping to open a new front in microplastic science: Researchers have been increasing their work enormously to understand how ingested Microplastic particles can affect the physiology and behavior of animals, but relatively little has been done to determine how those particles can affect structures built by insects such as caddis flies, bees, and termites.

The researchers used two types of plastic in this new experiment, polyvinyl chloride, which is known as PVC, and polyethylene terephthalate, or PET, a clear plastic used to make plastic bottles. In the laboratory, they cut the plastics into small pieces, which they mixed with sand in various concentrations. Then they let the caddis fly with larvae to do their thing.

The researchers discovered that the larvae used both types of microplastics to build their cases, especially in the early stages of construction. "We think it is because perhaps the plastic is lighter, so it is not that difficult to lift," says biologist Sonja Ehlers of the German Federal Institute of Hydrology, lead author of the article in the magazine. Environmental Sciences and Pollution Research. "And then the larvae start using those lighter materials instead of just choosing grains of sand."

Tamara Al Najjar

In fact, if you take a look at the image above, you can see that the far end of the case is almost all blue plastic. That was the part that the larva built first. As the larva grew, it was able to lift larger, heavier natural grains, making the pieces of the case closest to its head more gritty.

Tamara Al Najjar

Now take a look at this picture of the silk that holds the particles together. "In cases where there was plastic, the silk had more holes, and it wasn't as firm," says Ehlers. Furthermore, “plastic is a softer material than sand, and it is also lighter. And this could be one reason why if there is more plastic and less sand in the case, then it collapses more easily. ” Ehlers and his colleagues quantified this with a device that measures how much force is required to crush each case.

That's not a good thing, for the obvious reason that the caddis fly larva relies on the structural integrity of its case to protect itself from predatory fish. And it's potentially not good for more subtle reasons: the case helps camouflage the larva at the bottom of the river. That may not be a problem if the sediment the box is in is also filled with the same microplastics that the insect used to build its protective outer shell; it will still mix. But caddis flies often move around a river ecosystem, so if you end up in an area less contaminated with microplastics, or even plus contaminated with them, its color box could make it protrude. Increased predation in turn could affect the ecosystem as a whole, if the larvae cannot do their job cleaning the vegetation.

Being in close contact with the microplastic could cause physiological problems for the larva, since these materials are known to emit toxins known as leachates. "They also use the case for breathing," says Ehlers. “They are creating a flow of water inside the box so that the water passes through their gills. And so if there is embedded plastic, then of course those leachates could also get into the gills and cause some damage. ”

A longer-term concern, for caddis fly larvae and any number of other organisms at the base of food chains, is bioaccumulation. A small fish eats a larva, a larger fish eats the smallest fish, and concentrations of microplastics and associated toxins accumulate over time. The larger predators that people eat, like tuna, may be absorbing those microplastics and the chemicals they leach. We still need much, much more research on how microplastic contamination could be affecting different species, but the first indications are not optimistic. Recent research by scientists in the UK, for example, has shown that hermit crabs exposed to microplastics have trouble choosing new shells.

In addition to discovering the physiological effects of microplastics on organisms, scientists are only beginning to explore how species like the caddis fly behaviorally interact with the material, says University of Toronto ecologist Scarborough Scott MacIvor, who was not involved in this new job. but he has studied how bees are now incorporating plastics into their nests. Given how widespread microplastic contamination has become, the effects could be extensive.

"Animals are very likely to interact with plastics, which are having negative, neutral, and even in some cases positive impacts on their individual physical condition, more often than we think," says MacIvor. "We are simply not studying it. Rather we look beyond the goose sitting in its nest that is full of plastic straws and ropes and other anthropogenic materials. "

The pollution problem is only getting worse: According to consulting firm McKinsey, plastic waste can grow from 260 million tons per year in 2016 to 460 million tons in 2030. Even before the pandemic occurred, much of what " recycled "was never actually recycled. , and even more goes straight to the landfill now that the recycling facilities are closing. For a species like the caddis fly, microplastic particles can accumulate over time in their environment. Plastic, after all, is designed to be ultra-tough, so instead of breaking down entirely in ecosystems, it just breaks down into smaller and smaller pieces that turn into smaller and smaller cracks.

The most visible consequences of plastic pollution, such as whale stomach bags and six-pack rings around the birds' necks, remain a huge problem. Now researchers are digging deeper and deeper to show how ubiquitous little pieces of plastic are affecting animals at the micro level. Unfortunately for species like the caddis fly, there may be no escape.

This story first appeared on wired.com.