A cute and minimalistic fruit fly trap. No support needed. I recommend printing in bright, fruit-like colors to attract gnats and fruitflies much more effectively.

Perfect fit for those 90 cents shot glasses you can buy at Walmart. Here's the link.

The lid snap sturdily into place so the thing won't spill even if tipped over. The anti-tip base is optional, though recommended to increases stability. I also find that traps with bases has better visibility to the fruit flies and gnats.

You only need to pour a tiny bit of Apple Cider Vinegar inside (just a single teaspoon is enough). Then add a drop of dish soap to break the surface tension. The gnats/flies entered through the small opening and immediately drown the moment they touch the surface.