Sounds like a precision operation this wasp catching, will being one millimeter out make the trap useless or just not very efficient.?
It is a precision operation but it does depend on the nature of the food source. Food sources can be static or mobile and wasps employ navigational strategies accordingly. With static food sources (such as those found in a hive) wasps will return to within millimeters of the exact food source. Where the food source is mobile, for example people attending an outdoor display at a zoo, where those people have sweet foods but the locations of those foods is constantly roving within the display arena, then wasps will employ terrain navigation. Wasps will terrain navigate through flower beds for example because the position of blooms is contantly moving albeit within the defined flower bed.
It's not a question of the trap being useless or less efficient. It's understanding that wasps are programmed to ignore the trap if they have found and are already programme feeding on that original food source. To catch such wasps requires removing the original food source to break the programmed feeding behaviour to encourage the wasps to start looking for an alternative food source. Placing the trap in the exact location of the original food source means that the wasps won't have that far to go and so more of them are caught and eradicated (before they disperse) and if it's done properly then virtually 100% of those programme feeding wasps can be eradicated (rather than displaced to be a problem closeby elsewhere).
When it comes to wasp traps, efficiency and effectiveness are frequently confused. Efficiency is the proportion of wasps caught that are killed. High efficiency traps don't allow any wasps to escape and so prevent 'wasp recruitment' and therefore by definition will kill far fewer wasps but importantly, the traps themselves don't contribute to the problem. Low efficiency traps kill far more wasps but they still 'recruit' more wasps than they kill.
Effectiveness on the other hand is how good a wasp trap is at getting rid of the wasp problem. Unfortunately, effectiveness is the product of a multitude of factors which go well beyond the trap itself. The best way I have of describing it is to draw a parallel with a builders trowel. If a lay person buys a trowel should they expect to be able to build a house? The answer is no, of course not, and yet physically the trowel is arguably more simple in design than a wasp trap!
All of which means that people who use high efficiency wasp traps without understanding what they are doing won't necessarily get effective results (and so blame the trap) and those people who use low efficiency traps invariably don't measure effectiveness in terms of getting rid of a wasp problem (i.e. ending up with little or no wasps) they look for a busy trap that has killed lots of wasps as the measure of effectiveness (all the while still being plagued by wasps).
I know this may sound counter-intuitive but what's the purpose of a wasp trap? It isn't to catch wasps! It's to get rid of wasps and that's an entirely different proposition.
