Authored By Buggy Joe Boggs
Brood VIII (Eight) of the 17-year periodical cicadas (Magicicadaspp.) have made their presence known in parts of northeastern Ohio, western Pennsylvania, and the northern panhandle of West Virginia. As with past brood emergences, the overall geographical distribution is spotty; however, there are localized pockets with heavy cicada activity.
The general impact of a periodical cicada emergence can be divided into two "rounds." Round 1 starts with the emergence of huge numbers of males and females from the soil where they took 17 years, or 13 years for some broods, to develop. The males then "sing" to attract females for a love tryst. A behavior known as "chorusing" occurs when males synchronize their singing which tests the nerves of besieged homeowners. In short, a full-blown periodical cicada brood emergence is not subtle.
Mated females then use their spade-like ovipositors (ovi = egg, positor = deposit) to create slits and insert eggs into tree stems. This initiates Round 2 which is defined by the short-term and long-term damage caused by periodical cicadas. Although periodical cicadas have piercing-sucking mouthparts just like their aphid cousins, they cause no noticeable damage from their feeding activity.
The physical injury to the vascular and structural tissues of tree stems usually cause the affected stems to break-off and fall to the ground. This may happen immediately with attached leaves remaining green. Or, the stems may remain attached long enough for the leaves to dehydrated, wilt, and turn various shades of brown producing a symptom called "flagging" because it looks like small flags tied to the ends of the branches.
The cicada eggs hatch after a few weeks. The ultimate goal for the newly hatched first instar nymphs is to burrow into the soil to spend the next 17 years (13 yrs. for some broods) imbibing juices from tree roots. It is believed that twig detachment supports greater success and survival of the nymphs on their journey to the soil.
If heavy damage produced by the ovipositing females causes twigs to break-off and fall to the ground, the first instar nymphs just need to step-off into the soil. However, if twigs remain attached, the nymphs must drop from the tree canopy in a leap of faith aiming to land on soil that covers tree roots and not be blown off-course to drop onto a pasture, lake, parking lot, southbound freight train, etc.
The flagging may remain on the trees long after the cicadas are dead and gone. In fact, after Brood V emerged in 2016 which included a large part of eastern Ohio, I received e-mail messages well into August from Ohioans who had traveled I-70 asking why the oaks were looking so bad. It was cicada flagging damage that had never detached.
Cicada oviposition injury that was not severe enough to cause flagging may remain apparent for many years to produce diagnostic challenges. This is demonstrated by the images below.
Of course, the actual tree damage caused by periodical cicadas is considered minimal. It's long been recognized that although the flagging is very apparent, it causes no real harm to the overall health of established trees. In fact, it could be considered "natural pruning." Consider that periodical cicadas and their tree hosts have been living together for tens of thousands of years, and yet we still have trees.