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Half a century of caddisfly casings (Trichoptera) with microplastic from natural history collections
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Researchers examined natural history museum collections of caddisfly larval casings and found specimens from the 1950s and 1960s containing microplastic fragments incorporated into their normally organic-and-mineral construction. The oldest example identified pushes back the earliest documented occurrence of microplastics in freshwater invertebrate behavior into the mid-20th century.
Since the start of the production of plastic, synthetic polymers have littered our world. Early observations of this pollution, however, are scarce, and little is known of the history of environmental microplastics, especially in freshwater ecosystems. We studied this history retrospectively by analysing material from natural history collections. Since the 1950s, pieces of microplastic may have unintentionally been collected along with freshwater specimens. In the collection of Naturalis Biodiversity Center, Leiden, The Netherlands, we found early cases of animals that incorporated bits of plastic in their structures. Caddisflies are known to construct larval casings, normally made from fragments of vegetation or grains of sediment, but now that we live in the Anthropocene, caddisflies also have microplastics at their disposal as building materials. Here we present the oldest known casing of a caddisfly with microplastics incorporated, shifting the first known occurrence of this behaviour from 2018 to 1971, 47 years before the previous first reported finding. Tellingly, 1971 was also the year in which the first microplastics were discovered. The caddisfly casings examined here were not found in heavily urbanised places or polluted rivers, but in the springs of small natural streams with pristine groundwater, indicating that creeks were already polluted with microplastic right at the source. The particles suspected to be artificial were analysed with Energy Dispersive X-rays (EDX); this revealed titanium, barium, sulphur, zinc, chlorine, and lead - an elemental composition of common plastic additives in agreement with what has been previously reported for microplastics. Our study highlights the importance of the preservation of long-term time series in natural history collections and implies that microplastics have been impacting freshwater species for more than 50 years, and continue to do so on an increasing scale, as the amount of produced plastic keeps rising.
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High Density of Microplastics in the Caddisfly Larvae Cases
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High densities of microplastics were found embedded in the cases (shelters built from environmental debris) of caddisfly larvae, with plastics replacing natural materials like sand grains and plant fragments. This documents how widespread microplastic contamination has become in freshwater insect habitats and raises concerns about its effects on larval development.
Microplastic Footprint in the Larval Cases of Caddisflies (Trichoptera) for Tracing the Sources of Microplastics in Freshwater Bodies
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Scientists found that tiny aquatic insects called caddisflies unknowingly build microplastics into the protective cases they make, with some cases containing as many as 18 plastic bits. Since these insects are a key food source for fish and other wildlife, this discovery means microplastics are already entering the freshwater food chain, raising concerns about how these pollutants could eventually work their way up to the fish and water humans consume. The findings also offer a clever new tool: studying caddisfly cases could help scientists track down where plastic pollution is coming from in lakes and rivers.
Microplastics of different characteristics are incorporated into the larval cases of the freshwater caddisfly Lepidostoma basale
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Researchers found that the freshwater caddisfly larva Lepidostoma basale actively incorporated microplastics of various sizes, shapes, and polymer types into its larval case alongside natural materials, representing a novel pathway of microplastic interaction beyond dietary ingestion in aquatic insects.
A curious case: caddisfly cases built from brick and sewage overflow microplastics
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Researchers collected over 1,100 caddisfly cases from three locations in the Netherlands with varying levels of urbanization and sewage overflow pollution. In the most polluted stream, more than half of all cases contained artificial materials including microplastics from sewage overflows and brick fragments from urban areas. This is the first study directly linking sewage overflow events to microplastic incorporation in caddisfly cases, raising concerns about plastic transfer through aquatic food webs.
Preliminary indoor evidences of microplastic effects on freshwater benthic macroinvertebrates
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Researchers exposed caddisfly and mayfly larvae to various microplastic polymers in laboratory experiments and found that caddisflies incorporated microplastics into their rebuilt cases and mayflies preferentially burrowed in microplastic substrates over natural ones. The study suggests that freshwater macroinvertebrates may not perceive microplastics as a direct threat, raising concerns about chronic exposure effects in heavily contaminated waterways.
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When a large batch of papers lands in the Atlas, we read through it and send a short write-up of what stood out.