Although carnivorous plants do a wonderful job of catching and digesting insects. They should not be used for the purpose of eliminating insect problems. My plant collection outdoors has had a group of blue/black wasps visiting for several weeks now. I have only seen one of these wasps actually caught in a pitcher plant. I believe its capture was not due to it making the mistake of falling into the pitcher under normal conditions, but because it was raining and it was seeking shelter.
When I first noticed the wasps, there was only one in the area. Over the next several days, this number increased to as many as 5 of the same species of wasp. In this case, the plants actually increased the number of wasps in the area, no decreased.
This is also true of flies in my area. Although the plants capture many flies during the day, there are still hundreds to thousands flying around my plants. As an example, we had an outbreak of flies last week. I took my Akai Ryu Flytrap outdoors and within 20 minutes, each trap that was open (50+ on a double potted plant) had closed on a fly, and in some cases, two flies at once.
Ok, so the above examples are on plants kept outdoors with an unlimited supply of insects.
I also have some plants growing in a screen enclosed back porch. Only the smallest of flying insects, and possible crawling, can get through the screens. Because of the attractants these plants produce, I frequently have numerous flies and other insects sitting on and round the screens adjacent to my plant collections.
The only genus of carnivorous plant that I have found capable of capturing large number of insects and actually reducing the numbers is Drosera. I have virtually eliminated fungus gnat infestations with the introduction of numerous sundews in the surrounding areas of the infested plants. However, they have not caught a large number of house flies, if any.
If you do find a species of carnivorous plant that does a good job of eliminating insects in an enclosed environment, one must be able to then keep the number of insects entering that environment to a minimum or none. As long as there is a way for an insect to get in, they will be there, regardless of whats eating them soon after they take up residence.