I lived in Australia for several years and attended many a picnic or BBQ (and, no, there is no "shrimp on the barbie" because they eat prawns!). I noticed that at every outdoor meal, platters and plates of food were covered with mesh domes or tents to keep the pesky flies away.
These food covers are not common in America (on the East Coast, anyway). I find it interesting that in America, the world's most germophobic country (much to the detriment of our collective immunity!), we are pretty cavalier about flies! Of course, exposure to germs and bacteria is essential to building up one's immune system. But flies are downright nasty little critters: they not only transport harmful bacteria but they contaminate your food with eggs and maggots (ewww). So, I say it is time we Americans embrace the mesh food tent for all outdoor eating. These things are so great because they keep out the nasty pests, but you can still see the food underneath. And they are (usually) cheap and portable.
Mesa Home dome food cover with flip ring from Hayneedle
Zen Deluxe net plate covers made in Bali. Amazon
Inexpensive version from Amazon
, costing only $2.79 for a set of 2 (plus shipping).
Vintage Shoo Fly screen food cover from early 1900s from Antique Chasers
on Ruby Lane, $47.
Large Market Umbrella food tent from Sur La Table
, $12.99. This one is much bigger than the usual at 24" length x 20" width x 12" height.
Ming's Mark set of 7 pop-up collapsible mesh food covers plus 4 cup covers (so bigs don't get into your drinks! Pretty cool. Amazon
Party America colorful 3-pack from Amazon
This one is huge at 4 ft. x 2 ft. it covers an entire picnic table to keep flies, bees, and falling leaves off food. Big enough for large salad bowls, tall pitchers, trays, and all the fixings. Pops open for use, folds for storage. Harriet Carter
(Images: As linked above)