The combination of fall rains and warmer weather has helped encourage the wasps and rat populations to flourish. The last several summers have been rather warm and dry which has changed the comings and goings of pest. The sudden abundance of food and water this late summer, early fall has meant an increase in many pest populations, most notably rats and wasps. Rats restrict their breeding when times are hard as populations can better survive if they are kept small but once there is plenty of food and water their populations explode. Wasps also take advantage of the abundance of food and moisture. The late summer rains have brought abundance of vegetation, and with it, an outpouring in the number of insects on those plants. Wasps feed on plant nectar and on insects, getting plenty of protein and sugar. The result, much to the dismay of picnickers and gardeners everywhere, has been a magnanimous year for the pesky wasps.
https://www.linkedin.com/pulse/autumn-rains-bring-out-wasps-rats-randy-bilesky?published=t
http://www.delta-optimist.com/opinion/blogs/blog-autumn-rains-bring-out-the-wasps-and-rats-1.2359879