1. Swiftlets hunt flying insects in the air: flying ants, termites, flies, mosquitoes, planthoppers, weevils, ladybugs, damselflies, small stink bugs, moths, lacewings and many other small flying insects as prey. This is the only source of energy that gives swiftlets vitality and lets them fulfil the task nature has given them: to preserve the species, build nests from saliva, lay eggs, incubate them, feed their young and teach the chicks to eat. Through a special physiological mechanism that no other creature has achieved, swiftlets build their nests from saliva secreted by the salivary glands under the tongue. This saliva nest is a premium natural food that helps people improve their health and treat illness. Bats, swallows and many other creatures also eat insects, but they do not produce nests or any other product that is beneficial to nature and people.
2. Insects are a source of protein and chitin for swiftlets: under the action of various enzymes, insect remains are converted into nutritional energy sources including water-soluble glycoproteins and amino acids that keep swiftlets active. Chitin is converted into Chitosan/Glucosamine, an active compound for treating human bone and joint disease, which gives swiftlets the stamina to fly 300–500 km a day. Chitosan is insoluble in the water of swiftlet saliva, so once it is out in the normal environment it becomes a coating around the nutrients in the saliva and turns the saliva into long strands, giving the nest strands their toughness, even when soaked in water at high temperatures above 100°C.
3. Depending on the region of origin and the season, and on whether hard-winged or soft-winged insects are more plentiful, the amount of Chitosan in swiftlet saliva is greater or smaller, making the nest strands more or less tough; and depending on the degree of Deacetylation, Chitosan may or may not dissolve in hot water above 80°C. In the Central provinces, both island swiftlets and house swiftlets hunt insects along the hills and mountains of the Truong Son range. Insects in this region have wings and bodies covered by a thicker Chitin layer than insects in the Mekong Delta provinces, so nest strands in Central Vietnam are tougher than those in the South, but the amino acid and trace mineral content in the saliva is almost the same. The human body cannot fully absorb Chitosan unless it is converted into Glucosamine under the action of biological enzymes. The difference in toughness between island, Central and Southern nest strands comes from whether the insects' prey have more or less chitin in their body shells and wings. Swiftlets themselves cannot consume all this Chitin and excrete it.
4. Swiftlets in Southeast Asian countries are of a single species, C. Fuciphaga. The saliva of swiftlets in Indonesia, Malaysia, Thailand or Vietnam (in the Central or Southern provinces) is the same; there are no "young nests" or "old nests". Young swiftlets building a nest for the first time take more than 60 days to finish it, while later nests take 30–35 days. Nests that swiftlets build from saliva contain no toxins at all and no trace of toxic gas – 0 ppm – but if the place where swiftlets nest, such as the boards or concrete slats, has problems, the nests will be affected. Many nests have bases stained with the colour secreted by the boards, stuck with sand and cement from concrete slats, or contaminated with toxic gas from an unclean swiftlet house; such nests change colour and their strands become tougher. And when the strands are discoloured and tougher, at temperatures below 100°C double-boiling can hardly break down this tough membrane, so the absorption of the nutrients and active substances in the nest is limited and they are wasted and excreted.