Saliva’s Many Roles, From Boar Courtship to Nest-Making

To some saliva scientists, the human fluid is the main fascination. Others have dedicated their careers to comparing the glands of different creatures: spiny anteaters, bats, opossums, you name it. The glands are all so distinct, exalts Bernard Tandler, comparative anatomist at Texas Tech University in Lubbock.

They’re distinct in size: The elephant’s two main glands--the parotid glands--weigh more than 40 pounds apiece; those of little shrews and tiny bats weigh less than one-tenth of an ounce. But glands are also distinct in structure and function. Each creature, Tandler says, makes saliva tailored to its own unique needs.

The spit of a boar, for instance, contains testosterone to pique a sow’s interest when it’s showered over her during courtship. The spit of the short-tailed opossum contains chemicals used to mark its trails and territories.

The spit of a small bird, the swiftlet, contains a gummy glue that sticks its nest together (and is prized in Chinese cuisine for making bird’s nest soup).

Bats, Tandler’s particular love, make hefty use of tailored saliva. The spit of a vampire bat contains a protein--draculin--that stops victims’ blood from clotting during feeding. And many bats use saliva to identify kin.

“Think of a bat cave where there must be hundreds and thousands of bat mothers giving birth at the same time--they go out foraging and have to find Junior,” says Tandler. “How do they find him? By the characteristic odor of saliva.”

Tandler and his Texas Tech colleague Carleton Phillips have so far examined glands of about 300 species, including 240 types of bats. But the job is far from over.

“They’re all a unique story--every one of them,” Tandler says. “We’ve only scratched the surface.”