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Wednesday, October 20, 2021

How evil are weevils? A guide to managing pantry pests

Food infested with moths, weevils or other beetles can be a major nuisance, but experts say there’s no need to panic

A flour moth larva makes its way up a container of dried rice.
A flour moth larva makes its way up a container of dried rice. ‘Weevil’ is a catch-all word for pantry bugs, but there are several different species that infest Australian cupboards. Photograph: fadheit/Getty Images/iStockphoto

If you spot web-like filaments in your starchy pantry items such as rice, flour, oats or sugar, or bits of dry dust on shelves and holes in food packets, you could be facing an invasion of insects such as moths or weevils.

Among them you might see white moth caterpillars, which have an alarming resemblance to maggots but are a different species, or grain weevils, which entomologist and food scientist Skye Blackburn describes as “a tiny little beetle with a big long ‘nose’, kind of like Gonzo from the muppets”.

Beetle larvae are found inside whole grains, so you won’t spot those until you see the adults in the bottom of the packet. That applies to Sitophilus oryzae, the “rice weevil”, for instance, says Associate Prof Rob Emery from Murdoch University.

“It uses the snout to bore into the grain, turns around and lays eggs in the opening and seals the hole,” he says. “The egg hatches into a larvae, then generally stays inside the grain until it pupates.”

‘It’s all extra protein’

Usually people first notice an infestation when they see moths flying around the pantry or black weevils in stored food. Some weevil species even fly. This calls for immediate and thorough action – but they won’t harm you.

“It doesn’t hurt if you eat them and it’s all extra protein,” Blackburn says. “The average person will eat about a quarter of a kilogram of insects in their diet every year anyway!”

In fact, many cultures regularly eat insects such as crickets and beetles, and there’s a growing trend to cultivate them as a sustainable source of protein – Blackburn has even launched an edible bug business.

Typically, three types of insects get into pantries, according to Prof Ary Hoffmann from the University of Melbourne: grain weevils (mostly from the genus Sitophilus), flour beetles (Tribolium) and flour moth larvae (Ephestia or Plodia).

There are myriad species within these genera. The cigarette beetle Lasioderma serricorne, for example, loves chilli and other hot spices, according to Emery.

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“I stayed at a friend’s beach house and sprinkled chilli powder on my pizza,” he says. “The flakes looked a bit odd, so I opened the container and the chilli powder had been entirely consumed by the beetles, who then ate each other, leaving only the red wing covers [elytra] behind.”

Recently, a Perth-based TikToker made a similar discovery in her cayenne pepper.

Almonds with web-like filaments suggesting insect infestation

Web-like filaments or a dry, dusty residue are often the first sign of a pantry infestation. Photograph: lavizzara/Getty Images/iStockphoto

‘The problem is easily solved’

Generally, the eggs or larvae are likely to be present on the inside or outside of food packets bought from the shop. Once in your pantry, they can spread quickly – but don’t panic.

“The problem is easily solved and does not require the application of a chemical pesticide,” Hoffmann says. “All signs of life! And of course, the insects are interesting in their own right.”

If you find some moths, he adds, you could even take photos with a macro lens and admire the patterns on their wings.

For those who prefer to keep insects out of their food, there are several courses of action. If you already have an infestation, it’s time for a pantry spring clean. Inspect all your food for signs of the bugs. Note that you might also discover moth larvae in dried fruits, nuts, seeds, chocolate and dry dog food.

Rice weevils on milled rice
Rice weevils on milled rice. The insects may be troublesome, but experts advise against using pesticides to control them in your pantry. Photograph: TommyIX/Getty Images/iStockphoto

If you want to keep infested food, you can heat it in the oven to kill the bugs, Hoffman says. Home economics website the Spruce recommends roasting it at 60C for at least 15 minutes.

Putting produce in the freezer for 48 hours will also kill any eggs, larvae or adults, Blackburn says, and you can either pick out the insects, if preferred, or just eat them. To keep them from coming back, it is a good idea to vacuum the pantry and carefully wipe down all food items and shelves – top and bottom.

‘Look, buy, store, cook

To avoid future infestations, it is best to put everything in sealable jars – plastic bags are no barrier for the industrious insects. This is a great opportunity to organise your pantry and see what you have in stock, says Annika Stott, a sustainability strategist from OzHarvest.

Jars in a pantry
Putting pantry staples into airtight containers as soon as you bring them home from the grocery store is a good way to prevent an insect infestation. Photograph: Studio CJ/Getty Images

When buying dry goods, check the seals and the bottom of the bags for evidence of pests such as webbing, dry dust-like residue or tiny holes. When unpacking the groceries at home, put food into airtight containers.

Many people claim that repellents such as various dried herbs can help keep the bugs away. Hoffmann says he’s not sure how effective they are, but Blackburn swears by it. “Bay leaves are definitely a winner for me,” she says, “and it’s what I use in my cupboards at home.”

It is also prudent not to overbuy and stockpile food – the longer it sits in the pantry, the greater chance it has of attracting and breeding hungry bugs. That also raises the issue of food waste – as Blackburn says: “Our farmers work hard to give us food.”

On that note, the OzHarvest team has tips to avoid squandering precious food. Stott says their “mantra of ‘look, buy, store, cook’ is an easy way to get into simple habits to help prevent food waste at home and prevent pesky pests from getting into your food”.

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