>>1018435While this is a fair point, there is a fairly simple solution. Bug bivies are sold by various companies, usually in the $100 range for a professionally made one. Take a look at the black netting over my red sleeping bag in this picture.
If you have access to a sewing machine, you can manufacture your own out of bug netting, a zipper and a basic waterproof taffeta or ripstop (for the bottom) for well under $40. I cannibalized an old tent footprint that I never used and bought some mosquito netting and a zipper online for my first bug bivy. It ended up costing under $25 and it weighs around 4 ounces.
Another option is to sew bug netting to the edges of your tarp, which will keep out flying insects, although it won't stop spiders or other crawling insects from infiltrating. Tarp-tents are the next step - the airiness of a tarp, but full bug protection like a tent.
There are also a lot of trips where you won't need a bug bivy. For example, in the spring and fall, before and after a certain date, bugs won't be an issue by virtue of the temperature. Also, if you're not allergic to mosquito bites (like me), you can get bitten by them all night long and not develop any rashes. I've got plenty of blood to go around, and I don't expect mosquitoes in the high mountains to be carrying West Nile virus.
Depending on where you live, you will have to make your own decisions. In general, there's not a lot of deadly venomous creepy crawlies in high alpine terrain, so while I may get a spider going inside my sleeping bag sometimes, I've never gotten bitten by one and even if I do in the future, it wouldn't be a health hazard. Aside from mosquitoes (which a lot of people are allergic to), sleeping on the forest floor is really not THAT bad. For pic related, I had seen tarantulas crossing roads in that area pretty regularly, and while their venom wasn't going to kill me, their fangs are very sharp and large - a bite would have drawn blood. Hence why I used the bug bivy.
