Montgomery County says emergence of cicadas could trigger increase in rat population By FOX 5 DC Digital Team Published Montgomery County says the emergence of cicadas could trigger an increase in the rat population. ROCKVILLE, Md. - Montgomery County says the emergence of the 2021 Brood X cicadas could trigger an increase in the rat population. Health officials believe cicadas offer a food source for the rats while they are here and that the rodents could then continue to seek out other food sources in the same areas once the insects leave. During the 2004 cicada invasion, Montgomery County health inspectors say they received hundreds of additional residential and commercial rat complaints.