No, really, from a post I wrote:
Make Your Own Bedbug Detector
To make the detector, turn the dog bowl upside down to create a moat and a dome. Next, mix water, sugar, and yeast in the coffee cup, and rest the cup on the upturned bowl’s dome. The researchers covered the outside of their bowl in cloth tape painted black; bedbugs are attracted to the color. The cloth tape made it easier for the bedbugs to climb the sloping wall before falling into the well. To trap the bedbugs inside, the researchers coated the well with sticky resin. For DIYers, a sprinkling of talcum powder will make the walls of the moat too slippery to climb back out. In fact, talc is what’s used in the ClimbUp Interceptor, the most popular commercial bedbug trap on the market.
The Science Behind It
The researchers experimented with a variety of chemical bedbug attractants, but none were more effective than the simple DIY mixture. Bedbugs are drawn to the CO2 a sleeper exhales, and the combination of sugar, water, and yeast produces prodigious amounts of it — that’s how beer gets its fizz and bread gets its rise. Hungry bedbugs on the prowl for CO2 and human blood crawl up the sides of the bowl and fall down into the well, never to escape. The scientists used large quantities of sugar, water, and yeast to generate the CO2 in their experiments. Smaller amounts — such as those one might mix in a paper coffee cup — are safer, although may not be as effective.