Biologists on a trail in the Ecuadoran Amazon hold their breath as they distribute a foul-smelling delicacy to lure butterflies, critical pollinators increasingly threatened by climate change. A team has hung 32 traps made of green nets, each baited with rotting fish and fermented bananas.

They are meant to blend in with the forest canopy. Their pungent odor clearly does not. Since last August, a team of biologists and park rangers has been monitoring butterfly numbers in the Cuyabeno Wildlife Reserve, a park famed for its abundant flora and fauna.

Butterflies is seen in the protected Amazon rainforest of Cuyabeno, Ecuador.

A ranger inspects a butterfly.

A caterpillar walks on a tree in the protected Amazon rainforest.

Butterflies is seen in the protected Amazon rainforest of Cuyabeno, Ecuador.

Butterflies is seen in the protected Amazon rainforest of Cuyabeno, Ecuador.

Butterflies is seen in the protected Amazon rainforest of Cuyabeno, Ecuador

Biologist Maria Fernanda Checa holds an embalmed butterfly.

Biologist Maria Fernanda Checa holds an embalmed butterfly.

Biologist Maria Fernanda Checa holds an embalmed butterfly.

A ranger inspects a butterfly.

They catch and document the colorful insects, releasing most with an identifying mark on their wings. Some of them, possibly from previously unknown species, are kept for further study. The results of the team’s work, however, have been discouraging. Butterflies are “bioindicators,” living organisms whose well-being provides a measure of the health of their surrounding ecosystem, and their numbers are decreasing, biologist Maria Fernanda Checa told AFP.

While the number of species may not have declined by more than 10 percent, in terms of absolute butterfly numbers “the decrease is very significant... maybe 40/50 percent,” she said. “It is something that alarms us.”