"Place 1 lb of lingonberries or sauce in a suitable deep container (No. 10 can or equivalent). Fill with water to within about 1 in. from the top. Thaw the berries if frozen. Stir several times and pick out the larvae which float to the surface."
For everyone's comfort, I have deleted a few other extracts I found. But not this one:
"Spiny-headed worms (Acanthocephala). These worms live in the intestine and are attached to the wall by a protrusible proboscis covered with recurved hooks; the worms vary in length from less than an inch to more than a foot. The body of individuals from most species is elongate, flattened and capable of extension. No digestive tract is present at any stage of their life cycle; food is absorbed directly from the host's intestine.
If the average number of parasites found in the 3 subsamples is less than 2 per kg, the lot is considered passable."