Rats now outnumber people in south Tehran.
The rats, of the Norwegian type, have inhabited Tehran and many other Iranian cities for just the past 40 years.
Although the municipality kills close to one million rats annually, the number roaming the city is actually increasing, the Persian daily Jam-e Jam re ported.
Based on official figures, the rats outnumber citizens in southern Tehran by six times.
The pest's access to food has been restricted somewhat with the implementation of mechanized garbage collection. However, some citizens do not observe hygienic standards, leaving garbage along streets or throwing it in streams, thus helping to breed rats.
Furthermore, rats quickly become resistant to chemicals. Therefore, the type of pesticides must be changed annually.
Tehran's rats are 25 percent bigger than their global counterparts. In fact, some rats are even of the same size as cats. Hence, the municipalities cannot use cats for getting rid of rats.