As far as soldier fly larva, seems to work best in warmer months, where worms are better in colder climate. at least from my experience. Also, the larva seem to work much better when they are less mature, by the time they pupate or turn dark / thicker shell they are not as good of a bait. Therefore the soldier fly larva you get from the pet store (collected when the larva clime out of the bins to pupate) is not nearly as good.

For a year or so my daughter considered the earthworms her pets and I used the larva almost exclusively instead. I think it is very similar to horsefly larva which naturally grows in the lakes.

I try to keep the larva out of the earthworm bin, not only will they eat ALL of the food but when things heat up in the summer they can turn the bedding to slime and kill the worms very quickly.