Cockroaches have returned to Moscow while experts were guessing why – and where – the unwanted guests had apparently disappeared, the Moscow News reports.

Residents of Mal. Gruzinskaya Ulitsa were the first to witness thousands of cockroaches that suddenly appeared in the central area.

The reasons for the cockroach invasion are unclear, and experts say they did expect to see them again after a sudden disappearance but didn’t think it was going to happen overnight.

Professor Dmitry Mukha, the head of the laboratory for biological diversity, thought cockroaches would get used to the latest pesticides in five years time, he told Komsomolskaya Pravda just before the invasion.

“When they develop tolerance to these chemicals, a second wave will appear then,” he said, adding that his laboratory is currently working on the new remedy.

However, cockroaches decided to come back before the arrival of a new pesticide that would help humans win the war “for a long time, if not forever”, as the professor hoped.

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Source: Moscow News