Discovered mites in some flour!

Psocids in a bag of flour [click to see]Some time ago I opened a standard bag of flour that had been stored in the pantry [larder] for a week or two. I spotted that the top surface of the flour and the sides of the paper bag were hosting a few unwelcome guests in the shape of tiny wingless little grey bugs or ‘mites’ that were crawling around in an unsightly manner.

These >1mm long critters were not what you'd expect inside a new, sealed bag of flour. Anyway, the flour itself seemed fine (hmmm...?) so I evicted the bugs into the bin using a spoon and carried on as normal.  The same thing then happened again a week or two later, and then I found a few scampering around in the bottom of a nearby cereal packet as well. Could the bugs have come in with the flour? Was my pantry under siege?

These unsightly household bugs are called psocids (Liposcelis Bostrychophilia) and the fact that they like dark, warm, humid, powdery/ cardboardy/ papery sort of environments explains their alternative name of booklice. “These insects are normally regarded as pests of paper or cardboard packaging, and as such they are sometimes found in the packaging of dry foodstuffs,” advised the manufacturers of Homepride flour who confirmed that their premises are completely free of any such infestations (as one would expect).

[click to see]Homepride suggested that that infestation may come from cross-contamination of foodstuffs (or their packaging, anyway) during storage and distribution elsewhere in the supply chain, and this is something I can well believe after spending weeks cleaning out the pantry and everything that it contained, then repeating the process several times.

The presence of psocids is not at all due to lack of hygiene, I learned, and old and new homes alike can suffer from them. Independent research claimed that the kind of pest found in homes was not an issue in food factories or supermarkets, so it’s down to us householders to sort it out!

It seems psocids like to feed on starchy, moist foods and any microscopic fungal growths that naturally humid foods may spawn. Flour is ideal. They are particularly adept at migrating from old dry foodstuffs towards a new bag of eg flour which will be moist and fresh in comparison to any older stocks.  Information put out jointly by the Chartered Institute of Environmental Health and NABIM , the UK flour milling trade body, explained that psocids may live for up to six months and lay up to 100 eggs, preferring high humidity (kitchens are perfect) although  dry conditions can be tolerated for a while. Left undisturbed on the surface of older foodstuffs their numbers multiply rapidly in higher summer temperatures, resulting in their discovery in autumn after being incubated.

I also noticed how psocids would suddenly arrive from nowhere in the bottom of brand new cartons of breakfast cereals. They migrate from older locations and work their way through the dark nooks and crannies of carton ends (eg Weetabix boxes) or paper packaging (eg flour bags); the folds and tucks are very inviting and a few psocids can soon be seen wandering around inside new, unopened food cartons. One day I opened the pantry door and found a tiny crowd of the blighters had gathered in a plastic tray, but they fled in all directions because they hate bright light.

A flour mite action plan!

It takes time to fend off psocids so don’t expect overnight results when tackling them, and don’t be surprised if they return a few times before they’re gone for good (but even then, they may well return in the future). That’s partly because they can hide or lay eggs in all kinds of isolated nooks, including old packets of foodstuff or even the end grain of chipboard (as in, kitchen cabinet shelving).  But by working diligently the problem can dealt with if not eradicated altogether. The main point is, there’s no need to panic. I had two cupboards with the problem and here’s how I dealt with them.

Firstly, it seems a common way of treating foodstuffs like flour is to put the food in the freezer, which kills psocids outright. Myself, I’ve been happy skimming off the top layer of flour with a spoon, but you might want to freeze it to be sure. In one or two extreme cases I gave up and threw the flour away because the packaging was clearly contaminated – freezing might be the answer.

Next, I stripped the entire cupboard bare and cleaned everything with a hygiene surface cleaner spray several times. The shelves were removed and the ends of the (chipboard) shelves were liberally doused and cleaned, and allowed to dry. That’s because psocids will work into the exposed grain which is ideal shelter.

I removed all food from its cardboard packaging, especially breakfast cereal packets, and threw the packaging away.  The inner polybags were retained, using Klippits to seal them.  For some foodstuffs, eg more bags of flour, I chose clip-style BPF-free plastic storage boxes and found one type that fitted a 2lb bag of flour perfectly. This also stops cross-contamination between other food products. I chose to keep the flour in its packets but you might tip the contents into the plastic boxes. Also I cleaned and wiped down any eg plastic storage trays etc upon which food cartons and bags had been stored.

Main points to remember are to throw away all outer cardboard packaging (whether contaminated or not) and keep spraying and cleaning, and after several months of following this regime the psocids problem has diminished greatly, though the odd one still appears occasionally.  By following good storage and cleaning practices, I expect the problem will be eliminated but it will take a bit of time and dedication. Remember, they come in with packaging and can appear in the best-kept homes and kitchens.

Here are a couple of useful links, and the NABIM site has plenty of useful and interesting resources about flour:

• National Association of British and Irish Flour Millers - Psocids leaflet http://www.nabim.org.uk/psocids
• This pest control firm in Sardinia has a good write-up (English) though it refers to other (scarier) variants too -  https://www.galluradisinfestazioni.com/pests/psocoptera/liposcelis-bostrychophila

Comments and tips welcome below.