This section is from the book "The Balance Of Nature And Modern Conditions Of Cultivation", by George Abbey. Also available from Amazon: The Balance Of Nature And Modern Conditions Of Cultivation.
The House Martin (Chelidon or Cotile urbica) is of smaller size than the Common Swallow, which is rather more than 8 in., that of the former being about 5 in. in length. It arrives in this country about the middle of April and departs by the middle of October. The head and upper parts are coloured deep blue, the wings and tail are black, and the upper tail coverts pure white, as also are the under-parts. It builds its nest under the eaves of houses, in the corners of windows, etc.: hemispherical, formed of mud and lined inside with feathers, with a round opening for entrance. It lays five eggs, pinkish-white with an almost imperceptible dotting of red. About September immense numbers may be seen perched upon houses and trees preparatory to their departure; the food consists wholly of flies, gnats, and other insects.
The Sand Martin (Cotile riparia) is the smallest of British swallows, and usually is the first to arrive in Britain. It frequently builds in sandpits or gravel pits with sand layers, boring holes three feet or more in depth, and often winding in their course. Where a convenient sand-bank or cliff exists, hundreds of these little birds may be seen either working at their habitations or dashing about in the air. The eggs are five, pinkish white with an almost imperceptible spotting of red. The food is entirely insectivorous, chiefly flies and gnats.