The number of wasps in late Summer and Autumn depends on the number of new queens which survive the Winter, and the weather in Spring when the new queens are trying to start their new colonies.
A large number of new queens surviving the Winter will mean more competition for nest sites in spring, so the surviving queens will be in poorer condition and therefore fewer offspring will be produced in each nest.
A bad Spring means that many new nests will be destroyed, so fewer wasps are produced overall.
The best conditions for large wasp population numbers, and therefore the worst conditions for us in terms of wasp nuisance, are a dry and warm Spring, and fewer surviving new queens due to a cold and late Winter.
The new colonies will then be successful, producing large numbers of wasps. A single wasp nest will have thousands of inhabitants.
There can be more than a million wasps per square mile in the UK, which is a lot of wasps and all the traps and jam jars in the world won’t catch them all.
This is what makes Waspinator so good, it just alters their behaviour a little rather than trying to kill them all or get rid of all the wasps there are.