Carbon Dioxide Traps
by Joe Duff, WCEP

Whooping crane nest and decoy for black fly research with carbon dioxide traps
Photo: WCEP

How Carbon Dioxide Traps Work
Biting insects such as mosquitoes and black flies are attracted to our breath. People and animals exhale carbon dioxide (CO2) and that is how the insects find us so they can feast on our blood.
If you want to trap insects, you can produce carbon dioxide artificially and make the insects think they have found a whole crowd of people to attack.

Making CO2 Traps
There are several ways to produce carbon dioxide and make a trap. The simplest way is to use Dry Ice, which is frozen carbon dioxide. At minus 109° F, it is much colder than ordinary ice. Dry ice is the stuff you can put in a cauldron on Halloween so that it smokes like a witch's brew. As the Dry Ice you put into your trap begins to melt, it evaporates and attracts the insect—but an insect that lands on Dry Ice freezes instantly. Later you can collect the carbon dioxide traps and count the dead insects. This is how we find out how many insects—such as black flies—are around the Whooping crane nests.

CO2 Traps at Nesting Research Sites
The photo above shows one of the trap sites on the Wisconsin refuge where most of the eastern flock birds make their nests. Four of the seven traps have a fake nest. The nest has a fake egg, which has been rubbed on a real crane's preening gland for scent. A Whooping crane decoy (fake crane) sits on the nest, and a carbon dioxide trap is near. Traps, but no nests, are at the rest of the trap sites.
Twice a week at each decoy crane two glue boards are placed (one on the egg and one on the head of the decoy) for 5 minutes each.

By counting black flies at nesting sites and in other CO2 traps on the refuge, biologists can get data on black flies and decide how much of a problem they really are. If black flies turn out to be the main cause of nest abandonment, scienctists can consider what to do about it. They want to keep the refuge safe for all living things, while making Whooping crane reproduction more successful for this endangered species.

Journal or Discussion:

  • How would you explain the photo at the top of the page?
  • Why is it important for scientists to not jump to conclusions, but to gather data and do research before taking actions to control black flies?