Unfortunately, it will likely kill the snake if it is left there, so frequent monitoring is necessary. The birds will not return to the nest until the snake is gone, so the young may starve anyway. Could be a solution for the backyarder, if they remove the snake promptly. Either way, I would have a problem killing a snake; they are beneficial creatures too.
BlueBars

Netting kills birds, too. So really not so good an idea.

I've never seen the birds try to land on the pole under a nestbox, so I don't see how this could hurt the birds.

But I agree, this is best for backyard houses, in order to closely monitor and remove any snakes caught in the net.

Dee

Very Popular with Martin landlords in the deep south in order to protect there
birds. Where snakes are very common. May not be needed in northern tier
of states. I know they are problem here in Southern New England.
Black Rat and Racer snakes. Have been seen many times around box's and after
newly fledged chicks that cannot fly yet They really do
smell them it seems.
Ray

I had my male bluebird who was on the end of his thrid nesting in this box last summer, die in blueberry netting - 3/4" square black plastic netting. It was awful... I checked the net daily but ... it was not enough. I bought tobacco netting from a guy near Bradley Airport... and that should help. But I will not use this netting in my yard again. I will never forget that.

I don't see how a snake can get around the stovepipe baffle that is closed at the top except for the hole where the pole goes through.

Very easy for a five foot long snake to go right straight up most anything
PVC is the worst investment. Poles & post they wrap them self around pole
tighten and just go round and round simple for the free bluebird meal.
Had one get into a 14 foot high Martin house with 4 foot long PVC. The martins
moved to another house and re-nested. But that was a nightmare. I have removed all PVC from post. They smell the birds when they come out at night.

1/4" wire mesh is what I have been using. I fasten it around the pole and have never had snake problems. this youtube explains it well. Snakes cannot climb up the mesh and not even baby snakes can get through the 1/4" mesh. Put it on the pole and forget it. I'm in Maryland and my problem is black snakes.

Thanks for this post, Ray. We have a baffle, yet this spring's first clutch of bluebird eggs disappeared. It was during a very rainy spell, and I had not checked on them for a couple of days. When I did, gone! No pieces of eggs around the house on the ground, etc. However, in 2 day's time, other animals could have eaten the eggs, so it COULD have been a starling that I later saw reaching into the box. (We now have a guard on the front to help keep the startling from reaching the babies - I hope! We now have 2-day-old nestlings.) -PLEASE ** See my post if anyone can give input for me:

https://www.gardenweb.com/discussions/5334123/m=23/remove-dead-nestling

I'll check out that youtube about the wire mesh. I can't imagine the big snakes I've seen here not climbing right on/over anything stiff enough. We've been lightly spraying the pole AND baffle each evening with oil.

The netting sounds good to me, except I would be afraid finches or other "clinging" birds might get caught in it. ?

Sam, I watched the youtube - very helpful for rattlesnakes! Do you - or does anyone here - know if some larger snakes can/will climb right over the wire mesh? We don't have tons of snakes here, yet have found them over 6' long. Of course, one that long could likely reach up over our pvc-type baffle and many other things less than 3' (?) tall. I'm wondering if they would just slither right over a stiff mesh. Any ideas, anybody? ... Yes, still looking for a way to actually snake-proof the bluebird house pole without having to spray oil on it and the baffle each evening. ;)

In the previous post I show the wire wrapped around the post. Have not had trouble with snakes since I began using this.

The first batch of bluebirds fledged and are gone and box cleaned out. This morning I heard one adult singing up high and I assumed getting ready to start a second next so I checked.