At night, it creeps out of walls and drops on its victims, biting them while they sleep and infecting them with a disease that has no vaccine and no cure.
When they awake, its victims have a rash around the bite and a parasite in their blood that years later will weaken their heart, drain their strength and may eventually kill them.Chagas disease, a debilitating illness affecting up to 18 million people from Mexico to Argentina, is one of the worst of the range of maladies ranging from cholera to malaria that afflict Latin America's rural poor.
It is transmitted by the vinchuca, an insect the size of a cockroach that thrives in wood or adobe homes, especially those with dirt floors and farm animals nearby.
It infects people with a potentially lethal protozoan.
As health officials across South America take stock of Chagas disease's human and economic toll, they are stepping up efforts to wipe out the insect in a house-to-house war across six countries.
One battleground is the brushy hills north of Santiago, a tranquil area of olive groves and goat herds where residents say their homes were once full of vinchucas.
"Sometimes I would turn on the light at night and see vinchucas on the bed, on the walls, on the floor, everywhere," said Maria Teuquil who lives near Tiltil, 40 miles north of Santiago.
She and her two children have been bitten repeatedly and stand a good chance of being infected, though only a blood test will tell for sure.
Months have passed since she or her neighbors last saw the bugs. The Chilean government's anti-vinchuca campaign has come through the area showing people how to eliminate places where the insects breed, like cracks in walls and dirty animal pens.
Free fumigation as often as needed also helps, said the campaign's area director, Jose Antonio Segura.
His field workers have plastered schools and clinics with posters that sound more like a warning against a fugitive criminal than a tiny bug: "Vinchucas can kill. Report them - before it's too late."
Most victims never show symptoms and may not know they're infected - until a heart attack strikes, 15 or 20 years later.