The swallow's relationship to humans stands at the opposite extreme from the blackbird and house sparrow. Roman law, for example, was explicit that the swallow was not to be killed --they were associated with the household gods--and this taboo was commonly known in England into the 18th century. Indeed, widespread folk wisdom held that killing a swallow had evil consequences--cows, for example, might give bloody milk. (Swainson suggests that there was actually a fair amount of cultural variability in perceptions of the swallow). That swallows were entirely insectivorous had been definitively established by John Ray's stomach dissection studies. Aside from perhaps taking the occasional honey bee (Virgil's charge) the swallow was a decided good for agriculture.
Planters in North America were aware of the swallow's insect-eating habits from very early on; by the time of Mark Catesby's expeditions, farmers were already hanging gourds [Wilson suggests that the use of gourds was a Native American practice]to attract the swallow's larger cousin, the purple martin, to their fields. (Here the perceived benefit seems to have more the martin's tendency to chase off blackbirds than their diet per se).
Nevertheless, by the end of the 18th century even the swallow was subject to persecution. I've embedded below a widely reprinted piece by "T.H.W" that ran in The Gentleman's Magazine in 1790, on "The Utility of Encouraging the Breed of Swallows" [It begins on the bottom right of the page below; please scroll down to see it].
Citing the swallow's insect diet (good for both the farmer's crops and the prevention of annoying gnats), the author argues that the swallow should be protected "by the same popular veneration" as the Egyptian Ibis and the Dutch Stork. Although the swallow is not a part of the British diet (unlike the Continent), it has been the victim of hunters' target practice. The urgency of understanding the relationships between birds and insects is highlighted by the recent problems in North America with the hessian fly and its widespread destruction of wheat crops(T.H.W. cites the Annals of Agriculture). This is the spirit that would energize discussion of the topic in the U.S. agricultural press two decades later.
A response to T.H.W. the following month by "Benvoglio" elaborates on this topic, suggesting that other birds (as well as the hedgehog!) are not sufficiently acknowledged for their assistance in the garden.
Another response a few months later ups the supposed benefits provided by swallows and their kin:
What is at risk is not just crops but respiration itself! Here is the sentiment put to verse:
[This, by the way, is good evidence that bird protection as a public issue was building momentum in Britain as early as the 1790s]
It should also be noted that the widespread killing of swallows and martins as decorations for women's hats later in the 19th century was the original impetus for the series of Forest and Stream essays by George Bird Grinnell that would eventually lead to Audubon societies.
Next: Benjamin Barton and the House Wren