A flight interception trap (FIT), also known as a barrier trap, is simply some kind of barrier, such as a piece of screen extended between two poles or trees, that insects fly into, whereupon they fall into a pan or container of some type filled partially with a preservative. The barrier traps shown below were purchased as a unit, but one could just as easily make something just as effective. An alternative to screen would be plexiglass. The preservative we use is a 50/50 mix of low tox antifreeze (propylene glycol) and 70% ethanol with just a touch of dentatonium benzoate added to deter mammals or other animals from drinking it. Dentatonium benzoate is supposedly the most bitter compound known to man. At the very least it is not pleasing. We generally check these traps every 2 or 3 days. To check them it is useful to have some sort of strainer, or something similar to pour the liquid into. The accumulated insects (and miscellaneous leaves,etc.) can then be rinsed into a mason jar with a squirt bottle of 70% ethanol.

Barrier traps are useful for catching many small insects that are flying about and have a tendency to fly downward when hitting a wall. Malaise traps may be used as barrier traps as well, by simply placing pans under the central portion of the malaise trap.