Crickets munch on microplastics — especially if they have a big mouth

To a human, microplastics are very small at less than 5 millimeters (mm) wide. But to an insect, microplastics might be the same size as the food they usually eat. Researchers reporting in ACS’ Environmental Science & Technology have shown that crickets can and will consume polyethylene microplastics if their mouth is larger than the plastic particle. The study suggests that crickets — and likely many other insects — cannot distinguish plastic from food.

Previous research has shown that consuming microplastics negatively affects small animals like insects, snails and earthworms. These plastic particles, ranging in size from 1 micrometer (around the width of a bacterial cell) to 5 mm, are sloughed off a variety of sources like garbage and microplastic-contaminated fertilizer. Because of the plastics’ wide variation in size, it’s unclear how insects, which also vary in size, may respond to different particles. Crickets are “generalists,” which means they will eat almost anything that’s available — including plastic pieces. So, Marshall Ritchie and colleagues wanted to use crickets to understand how generalist insects interact with plastic-contaminated food as they grow.

First, the researchers gave groups of adult tropical house crickets (Gryllodes sigillatus) a choice between plastic-free food or food contaminated with either small or large microplastics. The crickets showed no preference for the uncontaminated food, but they consumed more of the contaminated food over time. However, unlike some other animals, eating plastic did not appear to stunt the crickets’ growth.

Next, the team investigated what sizes of microplastics crickets would consume over a seven-week period. During that time, the crickets’ body size increased by approximately 25 times, with their mouth size growing, too. The researchers found that crickets could only consume plastic particles whole when their mouth grew large enough. “Once a particle was big enough to be eaten, crickets continued to eat it for the rest of their life,” explains Ritchie.

The team also found that during digestion, crickets were able to break microplastics into smaller nanoplastics, which are more harmful to the environment than large microplastics. This ability changed as crickets grew — larger particles were found to be less fragmented in larger crickets.

The researchers say that this work suggests that crickets are unable to distinguish between plastic and food, and sheds light on the role insects may play in breaking down microplastics in the environment as they eat them and excrete smaller particles.  

The authors acknowledge funding from the Increasing Knowledge on Plastic Pollution Initiative from Environment and Climate Change Canada, and a Natural Sciences and Engineering Research Council of Canada Discovery Grant.

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