During autumn, the hornets shift from foraging and nest expansion to reproduction.
Research, external found that nests may produce up to 350 future queens and three times as many male hornets.
The newly fertilised queens will leave the nest and find somewhere suitable to surive winter, before starting new colonies in the spring.
In Alkham, Kent, inspectors have tracked a nest 30ms (98ft) up a tree.
Tracy Wilson, from the APHA, said: “At this stage the queen is almost certainly one queen, but as we move into the autumn more will be laid with the intention that those ones will then disperse.
“We need to get to those nests before the additional queens can disperse.”