I have not had a bug problem in my garden for 32 years and I never spray for bugs. I put up 25 bird houses and the birds take care of the bugs. I feed my birds well. There are a lot of online plans for wren bird houses but most of them wrens do not like. I built a lot of different designs and finally discovered what wrens like best. One place I read Wrens eat their body weight in bugs every day and another place said they eat about 1/2 their body weight in bugs so I don't know for sure which is true. Wrens love to sing.
1 The entrance hole should be small enough to keep out other birds other wise wrens will not make it their home.
2 The bird house must have plenty of ventilation.
3 The entrance hole must be facing south or a little south east.
4 The bird house must be about 8 feet above the ground.
5 Wrens will not stay in these unless you build several houses. A wren will typically built a nest in more than one house.
Build your bird houses out of pressure treated lumber other wise you will be building new replacement houses in about 3 years. You only need 1x4 and 1x6 lumber and some 1 1/2 inch long sheet rock screws.
Birds have a hard time getting tiny twigs, grass, sticks through a tiny hole so make your hole 7/8" tall by 3" wide. The wide hole also makes it easy for all the babies to feed at the same time. Wrens like a deep bottom house.
I like to make the pirch out of a forked tree limb.
The front of the bird house is a 1x6 board cut 7 3/4" long. The center of the hole is 2 1/2" down from the top. Drill two 7/8" holes about 2 1/8" apart then cut out the section between the holes with a jig saw.
The back is a 1x6 board 10 1/2" long.
The 2 sides are 1x4 boards cut 7 3/4" long.
The bottom is a 1x4 board cut 4 1/4" long. After cutting this board cut off the corners. Measure over 1/2" from each corner then draw a line at a 45 degree angle and cut on the line.
The top is a 1x6 board 7 1/2" long. I sometimes piece together a bunch of left over scrap pieces of wood to make the roofs.
Use the screws to attach the back and front to the sides. The bird house looks large from the outside but it is only 3 1/2 x 4 1/4" on the inside. The back of the house should hang over past the top and bottom so you can screw it to a tree or post.
Slide the bottom in to the opening and put a screw in each side.
Lay a 3/8" dowel rod on top for a spacer. Lay the top on the house and attach it with 2 screws. One screw in the front and one through the back. Slide out the dowel rod. This makes a vent at the roof.
Attach the pirch then hang the house 8 ft from the ground with the door facing south or south east.
This should solve all your bug problems. I use to have bird houses when I lived in Illinois and had no bugs. I have bird houses in TN and have no bugs here. My parents in Arizona have wren houses and they have no bugs either. I have relatives in NC with wren houses and they have no bugs in their garden. You need to get your houses up now or as soon as you can the birds have been checking out my houses since late Feb and they appear to be building nest now.
This is a different style bird house. Cut the front and back at 45 degree angles. Do not cut to a point leave the tip with a 3/4" flat for a vent. Then put on the roof so it has an over hang of about 3/4". The bottom edge of the roof should have a 1/4" space between the wall and the roof for a vent. Wrens like the hanging bird house better than the one that screws to a tree......probably 10 to 1 better. When you hang the bird house in a tree make sure there are no limbs or leaves or anything within several feet of the bird house. Make sure the bird house hangs on the lowest limb in the tree or make sure there are no other limbs under or at the side of the bird house other wise the birds will never live in it. Wrens are a little picky they don't like the house up too high about 8 to 10 ft is perfect.