We have an early season hiking area here (Henry Coe State Park) that is known for ticks. When I used a bivy sack with a bug net, I always managed to have several ticks attaching to me every day and at least one burrowed in deep. When I switched to a tent, fewer ticks, as long as I carefully removed then before I went in the tent, and none burrowed in. I really like the open feeling and star gazing with a bivy but now use a tent during mosquito season and anywhere there are ticks or biting ants. I have had a bear sniff my face when I cowboy camped, and it really was not too bad. I did, however, pack up and move a distance after that incident. One time I had bees swarm me while cooking and was really glad to have a tent to get into. You will inevitably occasionally get creepy crawlies if out in the open. Depends on how much that prospect really bothers you. And I agree with above posts. Really little point in a tarp and net if a tent weighs less. My bivy system weighs 1 lb 4 oz. My Tarp Tent weighs 2 lb 6 oz. The bivy is much more compact, so I can do an overnight with a day pack and there is no tent to have to set up. Nowadays with the light tents, it is more of a decision based on if you actually like to be out in the open.