Posted by Paul Callighan on May 08, 2024
2024’s emergence of two different broods of cicadas in the same year is unusual, but no cause for alarm according to Saint Charles Park District Naturalist Pam Otto who was this week’s Rotary speaker.  Brood 13 (locally) and Brood 19 (further south) will both emerge this year, but Otto showed Rotarians a penetration map indicating little overlap between the two (mainly in the central Illinois area).  “It’s not a cicada apocalypse,” said Otto.
 
Otto explained that a brood is made up of several species which emerge at the same time.  Over centuries, cicadas developed a timeline for hatching to disorient their predators by emerging on regular cycles while staying buried underground over multiple years.  Brood 13 is made up of three distinct species of cicadas.  The cicadas emerge as the ground warms to their desired temperature which will probably be in the next several weeks.
 
Once the cicadas emerge, they will begin a mating ritual according to Otto.  The male cicada seeks to attract a female using its “tymbal,” a membrane rubbed to produce a species-specific sound.  The sound is amplified through its shell that acts like a sound chamber.  The female uses a winged motion to acknowledge her suitor, creating a sound similar to snapping one’s fingers.  The life cycle of a cicada is only a couple of weeks.  Females lay eggs in slits made in tree branches.  After hatching, the cicada drops to the ground, burrows into the soil, and hibernates to await its appropriate timed emergence.
 
Otto gave a few thoughts on cicada’s impact on the environment.  She said it is common to see “flagging” where a branch holding eggs has a die-back reaction and turns brown as if it were broken .  There is soil aeration caused by the multiple cicadas burrowing for hibernation.  The decaying bodies of the large die-off can have a fertilizing effect.  And Ott pointed out that the cicada can become the meal of choice for birds and other predators that ordinarily might eat caterpillars, helping increase the butterfly population during their emergence period.