In previous episodes, we learned about accelerating Brood X cicadas, watched the emergence of cicada nymphs from their subterranean crypts, and discovered how male cicadas make their ethereal sometimes earsplitting sounds. To perpetuate their species, periodical cicadas depend on a bizarre survival strategy called predator satiation. In the entomological equivalent of a human wave infantry attack, vast legions of periodical cicadas overwhelm hordes of hungry predators by filling their bellies until they can eat no more. Although losses are enormous, when all of the gullets are filled, enough cicadas survive to renew the brood for another 13 or 17 years.
A band of hungry ants dismember a cicada during its molt to adulthood, a sad ending after spending more than a decade underground.
Scientists suggest the most significant ecosystem function provided by cicadas is the transfer of nutrients from the plant world to the realm of predators above ground. In my neighborhood where a boisterous emergence of cicadas is underway, predators are very busy in and around trees. While visiting with a birdwatcher this weekend, she remarked that sparrows, starlings, and grackles looked like they had just eaten a third helping at an all-night buffet. In addition to feathered reptiles, turtles are reported to snack on ill-fated cicadas that have fallen into water. Squirrels dine on cicadas above ground and small mammals like skunks may excavate nymphs in the soil. Cicadas are on the menu for pets as well, including cats and dogs. One owner claimed his pooch gained five pounds the last time periodical cicadas emerged.
Predators with backbones are not the only nemeses cicadas have to fear. A few weeks ago the vanguard of periodical cicadas began to emerge beneath my neighbor’s massive oak tree. Unfortunately, this tree is home to a healthy colony of carpenter ants on the prowl for arthropod meat in the tree and on the ground below. Many cicadas attempting to shed their skins and attain maturity were attacked and dismembered by this marauding band of six-legged predators. Fallen adult cicadas may be discovered and overwhelmed by fierce ground dwelling ants. Ants are not the only six-legged predators of cicadas. On one occasion I saw a stealthy predatory stink bug sneak up on an adult cicada resting on a branch. Although the cicada was many times larger than its foe, the stink bug delivered a perfidious kiss with its beak, immobilizing the cicada and allowing the stink bug to leisurely suck its blood.
Cicadas on the ground may be overwhelmed by ants.
In addition to vertebrates and predatory insects, cicadas face an enemy from a different kingdom – deadly fungi. The following account was reported in a previous episode of Bug of the Week during the emergence of Brood II in 2013: “Ahhh, but there is one patient nemesis of periodical cicadas that has evolved a diabolical plan for making the most of the cicada bounty. Beneath the trees where cicadas spend their youth sipping sap, spores of the fungal pathogen Massospora cicadina lay in wait for 17 years. During April and May, as cicada nymphs prepare for their escape from the earth, resting spores of Massospora adhere to the exoskeletons of the subterranean cicadas. Compounds on the surface of the cicada send a signal to the spores that dinner is served and it is time to germinate. Like an invading army, the fungus penetrates the skin of the cicada and multiplies, turning the cicada into a fungus garden. Spores of Massospora are then released into the environment where a second, more sinister wave of infection takes place. At this stage of their cycle, thousands of newly molted adult cicadas populate the landscape ready to begin the courtship ritual. Ubiquitous spores of the fungus spewed from the nymphs adhere to the skin of adult cicadas, germinate, and begin to infect the airborne legions.
The infection sterilizes both male and female cicadas, but does nothing to quell the libido of the sex-crazed male cicada. Infected males continue to seek and attempt to mate with females despite their contagious infection. In a game of tit for tat, female cicadas infected with Massospora remain attractive to healthy males that soon become infected as they attempt to mate with the Massospora Marys of cicada land. At this point, Massospora becomes a cicada STD and is transmitted from one cicada to another thereby increasing its numbers each day. In a short time, the infection turns the abdomen of the cicada into a buff-colored mass of fungus. Infected cicadas are flight capable and their peregrinations carry the fungus to new habitats as cicadas fly about. The fungus-laden abdomens of infected cicadas eventually drop off and inoculate the soil with the resting stage of Massospora that will await the return of the cicadas in 17 years. While the loss of an abdomen spells instant death for a human, this is not the case for a cicada. Throughout cicada land male and female Massospora zombies walk and fly about missing their abdomens, macabre reminders of a very clever fungus.”
Despite missing part of its abdomen, this cicada continues to walk about cicada land, spreading the contagious fungus.
The wonderful articles by K. S. Williams and C. Simon “The ecology, behavior, and evolution of periodical cicadas” and “Flying salt shakers of death” by Angie Macias were used as a resources for this episode.
Thanks to everyone who has participated in the Cicada Citizen Science project. With the Big Boy Band singing their hearts out in the treetops, more than ever we need to know if you have seen or heard cicadas. Please report your sightings at the link below.
CALL TO CITIZEN SCIENTISTS: We need your help! If you see periodical cicada nymphs, shed skins, adults on vegetation or on trees, and hear cicadas chorusing in the treetops, please report your sightings to magicicada.org. Cicada experts are attempting to map the distribution of these magnificent and magical insects. Thank you for your help.