The most striking observation was the difference in abundance of earthworms between cultivated fields and their uncultivated grassy borders....consider the living weight of the earthworms: an average of 78 pounds per acre within fields...and a maximum of 5,909 pounds per acre--in the grassy borders.Notably, as anybody who has ever dug worms for bait knows, some of the earthworms were likely to flee as the samples were being taking so the estimated high of 5,909 pounds per acre is likely to be low.
40 seconds of video showing footage of "leas", temporary pasture/hayfield being plowed. Footage taken somewhere in Britain. Note the dark soil which indicates a high organic content. When was the last time you saw birds following the plow like this? They tell us that this soil has a healthy invertebrate population.
The general rule-of-thumb used by folks who study this kind of thing is that the invertebrate biomass of all the other "bugs" is about 25% of the biomass of the annelids. Earthworms are just one, small twig on the annelid tree.
Thus, it is reasonable to estimate that fertile, well-watered soil that has been in "pasture plants" for multiple decades might have 1500 pounds of "bugs-other-than-worms" per acre.
That is a lot of bug!
It is also part of the attraction for the kinds of livestock that can harvest those bugs and turn them into eggs, drumsticks or fish fillets. Bugs are efficient at turning vegetation into animal biomass because they are cold blooded. They simply don't waste as much energy on maintaining body temperature. Another factor to consider is that they can harvest plant biomass that is below ground, something you cannot say about an Angus-Simmental calf.
As a point of reference, that same Angus-Simmental cross calf and her mother might produce 400 or 500 pounds of beef-on-the-hoof per year on that same acre. The shrinkage between the gate-and-the-plate is about 60% if you figure guts, hide, head and bones, so only 160-to-200 pounds of edible meat per year is generated off that pasture.
The issue is that most folks don't want to eat bugs but don't mind farm-fresh eggs or free-range chickens. Go figure.