Researchers at the Cary Institute for Ecosystem Studies, in upstate New York, comb the woods in search of ticks. Photography by Kirsten Luce

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This story is part of “Tickpocalypse,” a multi-part special report.

Kelly Oggenfuss is walking into the woods. Leading her team of four young researchers through a thicket of slender oak trees, she doles out assignments by letters corresponding to a grid. As early morning light filters through the canopy, Oggenfuss and her colleagues pull on latex gloves then disperse to gather surveillance data.

For 20 years, this has been a post-dawn ritual for Oggenfuss, a senior research specialist at the Cary Institute of Ecosystem Studies in Millbrook, New York, a bucolic town in the state’s Hudson Valley region. Four times a week from April to November — traditionally the most active tick season in the Northeast — she leads a platoon of field researchers as they don white coveralls, drive a pair of old Chevy Tracker SUVs down an overgrown dirt road, and hike to a five-acre tract designated “Henry Control” on the grounds of the institute. Their mission is to seek out and study ticks in one of the most tick-infested areas in America.

Oggenfuss and the others work methodically across a grid of 242 spring-loaded box traps, checking for rodents lured overnight by whole-oat…