There is currently not enough evidence to conclusively dismiss the technique as ineffective. Nor is there any scientific evidence to confirm that it works, or, if so, WHY it works. In fact, two scientific studies found that the technique did NOT repel flies and may have actually attracted more of the pesky critters. However, the studies have been criticized because they conducted the tests indoors under artificial light rather than in sunlight. Many commentators swear that the tip works. Just as many others dismiss it as ineffective.