When Packing Materials Become Pest Highways: Expanded Polystyrene
Written by Samantha Kiever
In a previous article, When Packing Materials Become Pest Highways: Biodegradable Packing Peanuts, we explored how stored product pests can infest and spread through shipments by feeding on starch-based biodegradable packing peanuts.
These materials were intended to replace the use of expanded polystyrene (often referred to by the trade name “Styrofoam”) packing materials, resulting in a reduced rate of plastic accumulation in our environment. After all, polystyrene is notorious for its persistence in the environment; it can take hundreds to thousands of years to degrade.
Still, if insects are your biggest concern, why not just use expanded polystyrene in outgoing shipments and request it in incoming shipments from vendors? Unlike biodegradable packing materials, expanded polystyrene is a plastic, leading many to assume it is impervious to insect attack. However, recent studies and our own observations in the lab suggest otherwise. Some insects are not only capable of consuming expanded polystyrene but can thrive on it, raising new questions about both waste management and pest control.
The Science Behind Styrofoam Consumption
In order to eat something, insects must have two things: the capacity to do it and the requisite behaviors to do it. Mealworms (the larvae of Tenebrio molitor) are known for being a stored-product pest with a voracious omnivorous appetite, though this is not their only noticeable trait. Mealworms are also known for their ability to chew through tough plastic packaging to get at the food within during storage thanks to their strong mandibles. As such, mealworms already display the capacity to chew plastic and the behavior of chewing plastic, and recent studies have been exploring their ability to eat plastic by studying their capacity to digest and extract nutrition from plastic – particularly polystyrene.
polystyrene with burrow hole and heavy grazing from Tenebrio molitor feeding
Their ability to extract nutrition from polystyrene comes from a unique symbiosis with bacteria in the gut that are capable of breaking down the strong bonds in the polymers of the plastic. In essence, the mealworms’ digestion of plastic functions much like a ruminant – they take care of bacteria in their guts that can break down the material to sustain themselves, and then the host organism gets the benefit of deriving energy from the bacteria’s activities.
Mealworms aren’t the only beetles cited with being able to derive energy from the consumption of expanded polystyrene. Red flour beetles (Tribolium castaneum) and confused flour beetles (Tribolium confusum) have also been reported in the literature to be able to utilize this common packing material for food.
Tenebrio molitor larvae amongst heavily degraded polystyrene
Observational experiments in the Insects Limited lab have confirmed these findings, suggesting that the ability to digest polystyrene exists in multiple populations and is not only confined to one stock.
To add fuel to this fire, there is also evidence that mealworms can digest polyethylene, a common plastic used in plastic shopping bags and packaging materials.
Packing Materials as Infestation Vectors
When an entity that doesn’t handle food sends materials to another entity that does handle food in some capacity, the shipments received are often not viewed with much scrutiny. After all, food-infesting pests require food to thrive. As such, it’s assumed that these incoming shipments are not potential vectors for pest issues. Shipments containing food or coming from other food-handling facilities are often inspected or monitored in some capacity for pest activity before being formally accepted.
Tribolium castaneum larva living on polystyrene
As discussed above, the risk of accepting non-food shipments with pests on board is higher than it seems on the surface. Both red flour beetles and mealworms have shown the ability to feed on various types of plastic, even in the absence of alternative food sources. These two species share a family, and if two more distantly related species in the same family have this same ability, what stops other storedproduct pests in Tenebrionidae from having or acquiring this same skill in the future?
This raises important considerations for both pest management professionals and the broader supply chain. Using expanded polystyrene as a "safe" alternative to biodegradable packing materials may not offer the pest-proof protection many assume. Instead, it might offer a low-nutrition, long-lasting buffet that actually encourages pest persistence and spread. Insect larvae that hatch in transit could survive long enough on polystyrene to reach a more hospitable food-rich environment such as production lines, warehouses, and storerooms.
Mitigation Strategies: Managing the Risk
Until such time as science turns pests into partners, facilities must stay vigilant. The same traits that make expanded polystyrene attractive for shipping—its durability, lightweight composition, and insulating properties—now come with hidden liabilities. Fortunately, there are several practical steps companies can take to mitigate pest risks associated with all types of packing materials:
Avoid Long-Term Storage of Packing Materials: Prolonged storage of any packing materials, especially in warm, undisturbed environments can create ideal harborage conditions for pests. Rotate inventory regularly and avoid stockpiling excess materials without a clear timeline for use.
Inspect All Incoming Shipments (Not Just Food): As demonstrated, pests can hitchhike in nonfood shipments, surviving on polystyrene or stowing away in packing voids. Incorporate pest checks into the standard receiving protocols for all deliveries, regardless of content.
Use Monitoring Devices in Shipping and Receiving Areas: Deploy pheromone traps, blunder traps, or other visual monitoring tools near loading docks and packaging material storage areas to monitor for pest activity despite a lack of traditional food sources.
A Double-Edged Sword: Pests as Pollutant Processors?
While the idea of insects feeding on expanded polystyrene raises serious concerns for food safety and facility sanitation, it simultaneously opens an unexpected door in the world of waste management. Polystyrene has long been criticized for its environmental persistence, often cited as a “forever” plastic with little hope of biodegradation. The discovery that insects like mealworms and red flour beetles can metabolize this material offers a potential avenue for reducing its long-term environmental burden.
These findings have sparked growing interest in bio-assisted plastic degradation as a complement to traditional recycling methods. If optimized and isolated properly, the bacterial symbionts that help these insects digest plastic could one day be harnessed in bioreactors or composting-like facilities to break down polystyrene and similar materials. In this way, a biological threat in one context may offer ecological benefits in another.
In the end, no packing material is without flaw. Biodegradable options come with the risk of being mistaken for food; polystyrene, long thought safe, now hosts a new class of opportunistic feeders. Recognizing that even our protective layers can become pest highways is the first step toward smarter, more adaptive pest management practices—ones that consider not only what pests do, but what they might evolve to do next.
Finding the Balance
At the end of the day, every packing material comes with trade-offs. Biodegradable starch-based peanuts may be more environmentally sound, but they offer pests a welcome meal. Expanded polystyrene lasts longer and resists moisture, yet it, too, is not beyond the reach of opportunistic insects. The choice between them is not just about sustainability or pest resistance, it’s about balancing risk, operational needs, and environmental responsibility in a way that best suits your facility’s needs.
Whichever option you choose, it’s clear that vigilance must accompany the decision. Insects are nothing if not persistent. Nature excels at finding a way to exploit even the narrowest niche, and what seems pest-proof today may be tomorrow’s pests’ lunch. By approaching packing material decisions with awareness and caution alongside strong inspection protocols, monitoring tools, and communication with suppliers, you can limit your potential for infestations while staying aligned with broader sustainability goals.
Because in the end, pests don’t need an invitation, just an opportunity. And they’re very, very good at finding one.
References
Abdulhay, Hind Suhail. "Biodegradation of plastic wastes by confused flour beetle Tribolium confusum Jacquelin du Val larvae." (2020): 201-206.
Fabreag, Mark Angelo C., and Joanne A. Familara. "Biodegradation of expanded polystyrene (EPS)(Styrofoam) block as feedstock to Tribolium castaneum (Red Flour Beetle) imago: A promising plastic-degrading process."
World News of Natural Sciences 24 (2019): 145-156. Przemieniecki, Sebastian Wojciech, et al. “Polyethylene, Polystyrene and Lignocellulose Wastes as Mealworm (Tenebrio Molitor L.) Diets and Their Impact on the Breeding Condition, Biometric Parameters, Metabolism, and Digestive Microbiome.” Science of the Total Environment, vol. 832, Aug. 2022, p. 154758, https://doi.org/10.1016/j.scitotenv.2022.154758.
Yang, Yu, et al. “Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 2. Role of Gut Microorganisms.” Environmental Science & Technology, vol. 49, no. 20, Oct. 2015, pp. 12087–93, https://doi.org/10.1021/acs.est.5b02663.
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