In Britain in the 1950s and 60s, the only commercially available live foods for insectivorous reptiles, amphibians and birds were mealworms and gentles (maggots of flies). The latter were only available in the fishing season and were not favoured by many reptile keepers. The word was about that they would chew their way into the gut wall after being swallowed. While this was probably not true for animals in good condition, the worry was always in the back of the mind. They were often the main source of food (but only in season) as hatched flies for chamaeleons and tree-frogs. Mealworms as well as being expensive were all I recall imported from the Netherlands and supplies and did not in arrive months. Home cultures were soon exhausted.
So what was used as livefood? The answer was earthworms. They could be dug for most of the year (hard frost as in the early months of 1963 was a problem) and in those days back gardens were big, not the pocket handkerchief-sized ones attached to new houses now). All my European lizards in the late 1950s and early 1960s were fed mainly on earthworms. They were kept in an outdoor reptiliary all summer and indoors in the winter.
Earthworms compare very favourably with mealworms and other insect livefoods; the protein content is similar, fat tends to be lower. I suspect that depending on the type of soil, earthworms were much better than insect foods because of the calcium in the soil that was traversing their gut when they were eaten. It is likely that Vitamin D would have been in short supply but being kept outdoors in the sun during the summer probably took care of that.