Why is my fish batter moving?

Saturday night is home-made fish and chips night at our place. I prepare the fish and my partner makes the baked potato chips with rosemary. For my part, the batter is prepared using stone-ground wholemeal flour and a secret mix of herbs and spices. Last Saturday the batter did not look right – it appeared to be moving.

Adult Confused Flour Beetle

Examination under a microscope showed the mixture to be chock-full of insects. I initially thought them to be weevils but a closer look revealed them to be adult and larval Confused Flour Beetles (Tribolium confusum), not as confused as me I can assure you. And they are tiny. In the pictures, the size of the larva and the adult beetle can be compared to the nearby stone-ground flour particles.
Worldwide, these beetles are a major agricultural pest and are highly resistant to pesticides and radiation. They cannot feed on whole grain but readily feast on grain dust, flour and broken grain. The ‘confused’ name

Larval Confused Flour Beetle

comes from the fact that they are often mistaken for other common flour beetles, particularly the Red Flour Beetle (Tribolium castaneum). They can be distinguished by the shape of their antennae.
As I have had this flour for a while, the question in my mind is ‘Why has this infestation happened now?’ Of course the other question, which doesn’t really bear thinking about, is ‘How long have I been cooking with beetles without even knowing!?’