MISSION, Tex. — Last month, Marianna Wright, the executive director of the privately owned National Butterfly Center here, discovered survey stakes on the property marking out a 150-foot-wide swath of land.



Ms. Wright later encountered a work crew cutting down trees and brush along a road through the center. The workers said they had been hired by United States Customs and Border Protection to clear the land.

“You mean my land?” Ms. Wright asked, before kicking them out.

A few days after that encounter, she was visited by a border official who informed her that the crew had a right to be on the land and would be returning — next time accompanied by armed Border Patrol agents.

She said she also learned, for the first time, that a section of the proposed wall on the border with Mexico — and a pair of parallel roads on either side of it — would run through the butterfly center, a nonprofit organization dedicated to the conservation and study of wild butterflies.. The wall’s placement would cut off two-thirds of the center’s property, leaving a 70-acre no man’s land between the wall and the Rio Grande.