When you find pests in unopened packagings, the explanation might be that they arrived with the goods. However, it is also a possibility that they have penetrated through the packaging either in the storage, the store or at the customers’ homes. But no matter how it happened the consumer will inevitably make the manufacturer responsible for the pests’ presence.
It is therefore not sufficient to ensure that the product is free from pests when it leaves the factory. One must also seek to protect against invasions during storage and distribution. This is partly done with appropriate packaging.
Some insects can bite into the goods through containers of paper or plastic – the lesser grain borer, the cigarette beetle and the bolting cloth beetle – that are pests that are not very common in Northern Europe. Gnawings on packagings are due to more common pests that have eaten their way from the inside out. Moth larvae will often gnaw their way out of the package in which they lived before they pupate. Newly hatched drugstore beetles can chew through the packaging through small circular holes.
Bacon beetles and other beetles of the genus Dermestes likes to chip away in cardboard or other semi-soft materials, such as wood, before they pupate. Skin beetles that might have lived in a batch of dog food can do secondary damage to consignments stored nearby.
It is therefore very few insects that can gnaw into a packaging from the outside, but many are able to force their way through small leaks in packaging. It has been calculated that 3/4 of all invasions happen this way.
Adult insects often lay their eggs in cracks or holes in the packaging, where the scent of the product leaks out. When the eggs hatch, the quite small, active larvae squeeze their way through very small cracks. Invasions of moths, drugstore beetles and saw-toothed grain beetles frequently happen that way. Metal cans and glass with tight fitting lid are probably the only packagings that provide 100 % protection against insects and mites.
Hessian, cotton, rayon and other textiles protect poorly and even worse, as the weave is looser. Most of the pests that seek out foods can squeeze through the mesh or find adequate holes at closings and seams.
Tightly woven cotton bags can be done almost insect proof for up to six months when the seams are secured with tape and surface-treated with an insect repellent agent with pyrethrin and piperonyl butoxide.
Paper and cardboard provide better protection against insect infestations than textiles. Dense paper packaging protects against pests that cannot gnaw their way in, and provides some protection against less efficient rodents. The thicker the paper packaging, the more protection. Saw-toothed grain beetles may penetrate through a single layer of thin paper, but they will rarely be able to penetrate thick paper. The weak points of paper packaging are closings such as stitching in paper bags. Cardboard which offer good protection against most pests has weak points where the package is folded and glued. A powerful tape at closings and folds can make cardboard packaging virtually insect proof.
Cellophane is similar in strength to thin paper. Cellophane packaging is often ruined by cockroaches.
The advantage of plastic film is that it is usually easy to seal products completely, e.g. by heat welding. Such undamaged packaging provides safe protection against all the non-chewing insects. Metal foils are more resistant to chewing insects than paper and plastic, but they are not insect-proof. Pests as the lesser grain borer and grain rodents go effortlessly through an aluminium foil.
Peculiar findings of insects in foods, such as earwigs in spirit or woodlice in a glass of aspirin, are in many cases due to pests having strayed into the packaging at the storage. It is therefore important to retain the packaging in rooms which can be kept free from invasions of pests from the outside.