This Tiny Creature Seemed Extinct. DNA Technology Helped Prove It Wasn’t.

“We know from ‘C.S.I.’ that we leave DNA everywhere,” said Sean Rogers, a biologist at the University of Calgary who published a review of eDNA technology in November. “With conservation it became — instead of taking nets to try to capture fish or hoping to catch something on a wildlife camera — let’s take forensics one step further.”

Instead of digging, splashing and scraping to quantify a species’ survival, ecologists can now sample air, water, soil and even the built environment — anywhere a living creature might scrawl its genetic signature with secretions, skin or other scraps of DNA.

From there, researchers isolate any distinct DNA and compare it with known genome sequences. An organism’s DNA can last from a few hours (in the case of certain freshwater crustaceans) to thousands of years (as seen in 13,000-year-old giant ground sloth bone fragments or half-a-million-year-old permafrost-captured horse bones).

This type of genetic sleuthing has helped researchers monitor endangered species, such as Vietnamese crocodile lizards, Australian sea lions, Swedish pool frogs and Canada lynxes. Last fall, researchers even analyzed eDNA to rule out theories about the mythical Loch Ness monster. (What they found was evidence of lots of eels.)

Because eDNA techniques are less destructive and more efficient than classic surveying methods, they have become popular for examining elusive life-forms: emergent invasives, endangered species or otherwise scarce and secretive creatures.

Take the Rio Grande siren, a cryptic and nocturnal salamander that spends its days hiding in mud. In vain, scientists have baited siren traps with bacon, shrimp and chicken liver, then waited months to catch a single specimen, said Krista Ruppert, a biologist at the University of Texas Rio Grande Valley.

“We don’t know much about them because they’re traditionally difficult to study,” Ms. Ruppert said. Now, scientists only need to analyze water samples for siren eDNA: “You don’t have to see it to know it’s there.”