Pestology Blog

When the Magicicadas, more commonly known as the periodical or 17-year cicadas ,last emerged in 2004 in the Maryland area, I was approximately 10 years old. The entire event blew my mind. I’m not saying that it was instrumental in eventually making me an entomologist (I mean, after all, at that age I would have told you very confidently that I wanted to be a marine biologist), but it’s pretty up there. Needless to say, I was just as excited (if not more), when their mass emergence came back around in 2021.

Individuals who were equally as excited about the return of the Magicicadas were two of my former advisors, who recently authored a paper examining the effects of the mass emergence of the Magicicadas on the ecosystem. The mass emergence of the Magicicadas provides the environment with what is called a biomass pulse, which means that a huge amount of nutrients are suddenly available in the environment. Previous work studying the biomass pulse of the Magicicadas had documented the benefits to the soil in terms of the nutrient addition thanks to the decomposition of their bodies. However, there was not a lot of research done on the other aspects of the food web, including how the Magicicadas may influence predation levels and how that may cascade throughout the ecosystem.

Magicicadas are a genus of cicadas that consists of several species with the unique (and very slow)development time of either 13 or 17 years, depending on the species. In an emergence year, the nymphs will emerge from their underground burrows in the billions around springtime and will molt into winged adults. The males will head to the trees to try and attract mates. They do so by creating noise to attract females, or, as I affectionately refer to it, screaming about how great their genes are. Once they have successfully mated, the female will lay up to 500 eggs in the twigs of trees. Both parents will die quickly after mating. The eggs will hatch in the twigs, and the nymphs will feed on the tree twigs until the later summer. At that point, they will emerge from the twig and drop to the soil, where they will continue feeding on the roots until their emergence comes around again.

Specifically, this study focused on the effects of the mass emergence of the Magicicadas on birds, caterpillars, and trees. This includes the major players in each part of the food web in the forests of the eastern United States where Magicicadas grace us with their presence. First, the researchers performed field observations to confirm that birds were, in fact, feeding on the cicadas. They were able to document 82 different species of birds that were feeding on the Magicicadas. In addition, it was also an extremely wide array of species, which suggests that different insect-feeding birds from different ecosystems were taking advantage of the resource pulse that the cicadas provided through their mass emergence.

Next, they examined how the emergence of the cicadas affected the way that birds foraged for their normal foods-in this case, caterpillars. They did so by placing model caterpillars in the wild to document the frequency of bird strikes out in the forests in the summers of 2020, 2021, and 2022. Overall, the researchers determined that bird strike frequencies declined immensely in concurrence to the 2021cicada emergence. In addition, they also surveyed trees throughout these same time periods, and noted that the abundance of caterpillars also increased significantly in 2021. This suggests that birds arechanging their usual foraging strategies to eat the Magicicadas, when they are available.

Lastly, the researchers also looked at the levels of leaf damage to trees between 2020, 2021, and 2022.There was a significant difference in the amount of leaf damage in 2021 compared to the other two years. Therefore, the increase in caterpillars caused by the lack of normal predation by birds indirectly caused damage to trees. Previous studies have shown that higher herbivory can cause serious problemsfor trees, such as lowered reproductive ability, lowered immunity to pathogens, and more.

What this study found overall was the mass emergence of the cicadas directly changed the way that the birds were foraging, which increased the number of caterpillars. The subsequent increase in caterpillar populations thanks to the lack of predation by birds led to an increase in tree damage. In other words, the mass emergence of the Magicicadas the power to “re-wire” food webs, both in their emergence year, and beyond.

In terms of pest management, understanding how these “pulses” of these potential resources affect an environment can be extremely helpful. For example, many bird species are responsible for pest-reduction services through predation, but if these predators are “distracted” by a resource like cicadas, it could have implications for how we implement pest management strategies. In addition, understanding these resource pulses in the ecosystem may help us predict other pulses in the environment-such as an increase in cicada killer wasps, thanks to the abundance of their food source during an emergence year. The moral of the story is that the Magicicadas just don’t cause a sonic annoyance and damage a few trees every few years. In fact, we are just beginning to appreciate how impactful their mass emergence is to their ecosystems, and how those effects may radiate out throughthe environment. In other words, not only are the Magicicadas cool, but their effects on the environment are also arguably just as cool as they are.

...is it 2038 yet?

Article by Laura Rosenwald, BCE

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