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The caddis fly larvae crawl along the river bottom of the world and suffer from an ongoing housing crisis. To protect themselves from predators, they collect grains of sand and other sediments and glue them all together with silk to form a cone that holds their worm-like bodies. As they mature and lengthen, they have to continuously add material to the case. Imagine adding spaces to your home for the rest of your life, or at least until you turn into an adult insect. If the Caddis fly larva somehow loses its case, it has to start over, and that's a pretty precarious situation for a defenseless meat tube. And now the microplastic threats are piling up on the list of caddis diseases.
Microplastic particles – pieces of plastic less than 5 millimeters long – have already damaged many environments around the world, including the formerly untouched sediments of the Arctic and the deep sea. In a study published last year, researchers in Germany reported that they found microplastic particles in caddis flies in the wild. Then, last month, they published the worrying results of laboratory experiments, which found that the more microplastic particles a Caddis fly larva included in their case, the weaker the structure. This could open caddis flies for greater predator farming and send wave effects through river ecosystems.
Some examples of caddis fly cases. Image A was collected from the wild and B was built from a larva in the laboratory out of sand. In picture C the larva has built in black PVC particles. And in D they are blue PET particles.
Tamara Al Najjar
You may be wondering why an insect species is important. But caddis flies are critical actors in these ecosystems, and their struggles could well have ramifications. Caddis fly larvae are working on an important gig that sucks in the aquatic vegetation and prevents a river from becoming overgrown. As flying adults, they serve as an important food source for bats, frogs and spiders. This study also helps open a new front in microplastic science: the researchers have massively intensified their work to understand how microplastic particles ingest can affect animal physiology and behavior, but relatively little has been done to determine How these particles could affect The structures that insects such as caddis flies, bees and termites build.
The researchers used two types of plastic in this new experiment: polyvinyl chloride, which you know as PVC, and polyethylene terephthalate, or PET, a clear plastic that plastic bottles are made of. In the laboratory, they chopped the plastics into tiny pieces, which they mixed with sand in various concentrations. Then they let the caddis fly, larvae do their thing.
The researchers found that the larvae used both types of microplastics to build their cases, especially in the early stages of construction. "We believe that this is because the plastic may be lighter and therefore not that difficult to lift," says biologist Sonja Ehlers from the Federal Hydrological Institute, lead author of the paper in the journal Environmental Science and Pollution Research. "And so the larvae start using these lighter materials instead of just choosing grains of sand."
Tamara Al Najjar
If you look at the picture above, you can see that the other end of the case is made almost entirely of blue plastic. That was the part that the larva first built. As the larva grew larger, it was able to absorb larger and heavier natural grains, which is why the parts of the casing that are closest to its head are sandy.
Tamara Al Najjar
Now look at this picture of the silk that holds the particles together. "In cases where there was plastic, the silk had more holes there and was not as strong," says Ehlers. In addition, “plastic is a softer material than sand and is also lighter. This could be a reason why it breaks down more easily when there is more plastic and less sand in the case. “Ehlers and her colleagues quantified this with a device that measures how much force is required to crush each case.
This is not a good thing, for the obvious reason that the Caddis fly larva relies on the structural integrity of its casing to protect itself from predators. And it may not be good for more subtle reasons: the case helps camouflage the larva on the river bottom. This may not be a problem if the sediment in which the housing is located is also littered with the same microplastics with which the insect has built up its protective outer layer. it will still fit in. But caddis flies often move in a river ecosystem. So if you land in an area that is less or even more contaminated with microplastics, it can stand out due to its colored housing. Increased predator farming could in turn affect the entire ecosystem if the larvae are unable to clean the vegetation.
Such close contact with microplastics can cause physiological problems for the larva, as these materials are known to emit toxins known as leachate. "They also use the case for breathing," says Ehlers. “They create a flow of water inside the case so that the water flows through their gills. So if plastic is incorporated, this leachate could of course also reach the gills and cause damage. "
A longer term problem for the Caddis fly larvae and any number of other organisms based on food chains is bioaccumulation. A small fish eats a larva, a larger fish eats the smaller fish until it stops, and the concentrations of microplastics and the toxins associated with them accumulate over time. The larger predators that people eat like tuna may absorb this microplastic and the chemicals that leach it out. We need a lot, much more research on how microplastic pollution could affect different ways, but early signs aren't rosy. For example, recent research by scientists in the UK has shown that hermit crabs exposed to microplastics have difficulty selecting new shells.
In addition to studying the physiological effects of microplastics on organisms, scientists are only beginning to investigate how species like the Caddis fly interact with the material, says Scott MacIvor, an ecologist at the University of Toronto at Scarborough, who was not involved in this new work but has investigated how bees are now incorporating plastics into their nests. Given the ubiquitous pollution from microplastics, the impact could be significant.
"It is very likely that animals will interact more often with plastics that have negative, neutral, and in some cases, positive effects on their individual fitness than we think," says MacIvor. "We just don't study it. We look past the goose sitting on its nest, which is full of plastic straws, cords and other anthropogenic materials. "
The pollution problem is getting worse: According to the consulting firm McKinsey, plastic waste can increase from 260 million tons per year in 2016 to 460 million tons by 2030. Even before the pandemic broke out, much of what you “recycled” was never recycled, and even more goes straight to the landfill after the recycling facilities are shut down. In a species like the caddis fly, microplastic particles can accumulate in its environment over time. After all, plastic is designed to be extremely tough. Instead of completely decomposing in ecosystems, it only disintegrates into smaller and smaller pieces that pass into ever smaller angles.
The most visible consequences of plastic pollution, such as sacks in the stomach and six-pack rings around the birds' necks, remain a massive problem. Now researchers are digging deeper and deeper to show how tiny, ubiquitous pieces of plastic affect micro-level animals. Unfortunately, there is no escape for species like the caddis fly.
This story first appeared on wired.com.