Answering Brood X cicada lingering questions – investigating the reasons why some areas did not see them this year

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FORT WAYNE, Ind. (WANE) – You have cicada questions, we have answers. WANE 15 spoke to Dr. Elizabeth Barnes, the Exotic Forest Pest Educator at Purdue University, to help answer questions about the Brood X cicadas. She offers her knowledge and expertise looking back on this year’s emergence.

Why did some locations not see the Brood X cicadas?

There are three main explanations why a given location did not see the Brood X cicadas this year. First, it is possible a place does not have a good cicada habitat. Second, it is possible a location used to be a good cicada habitat, but construction and human development since the last emergence of the Brood X cicadas 17 years ago has made the habitat no longer suitable; their food source could have been removed. The last explanation is what scientists are interested in figuring out: why did an area that saw cicadas 17 years ago not see them this year?

Researchers are working on papers to understand which explanations are the most plausible for this last category. It is the goal to have confirmed answers within the next one to two years. A Citizen Science mapping program is also being conducted to help uncover where the cicadas emerged this year and answer the question of where they are and are not located.

Is there a connection to the weather?

The peak emergence period for the Brood X cicadas is normally from late April through early June, but can still occur from the beginning of April to late June. This is during a stretch of spring that typically features big swings in the weather conditions. The Brood X cicadas usually need temperatures eight inches below the ground to reach 65 degrees before they start to emerge. They also like to emerge right after a warm rain. The cicadas are not impacted by the severity of the winter and the heat and humidity of the summer.

This year, it was a warm start to the spring. Dr. Barnes says reports of cicada holes near the surface were received early in the spring, indicating the Brood X cicadas were on the cusp of emerging in early to mid-April. High temperatures in Fort Wayne were in the 70s to 80s from April 4th to April 10th. Rainfall of 0.43 inches was recorded on the last day of this stretch. However, by later in the month, temperatures plummeted, with highs in the lower 40s on April 20th and April 21st. A snowfall of 4.2 inches occurred on April 20th.

It is this combination of a warm start to spring, followed by the cold, that may have spelled trouble for the cicadas. While it is unsure if the cold itself could have killed the cicadas in some locations, the fact many of them were close to the surface so soon exposed them to other things that could kill them. They were at risk of predators eating them or their burrows getting flooded. Some cicadas may have returned back deep underground and not have emerged.

Another weather condition that may cause trouble for the cicadas is strong winds knocking them off of trees. They can fall and die on the ground, or the cicadas’ delicate eggs can break when they fall to the ground.

Is there a reason the Brood X cicada may have avoided emerging in urban areas?

The Brood X cicadas do not like urban or developed areas. They only move a short distance on the surface once every 17 years and they only move one meter underground. Therefore, they can build up and grow their population numbers easier in undisturbed areas. The longer an area remains undisturbed, the more the population grows as more cicadas breed and lay their eggs. Trees need to be undisturbed for at least 17 years for a population to build up in a given area.

Human activity, including the removal of trees and the turnover of soil, can destroy Brood X cicada populations. The loss of trees means a loss of habitat. If the cicadas get turned toward the surface in the soil, they become easy pickings for predators or are crushed. The use of pesticides is also dangerous for the cicadas.

Based on human activity in urban or even suburban areas, the cicadas therefore may have been seen more often in more rural locations.

Why did seasonal cicadas emerge but not the Brood X cicadas in some areas?

You may still be encountering the seasonal cicadas in an area where the Brood X cicadas were not seen. Why is this the case? As Dr. Barnes explains, seasonal cicadas are more resilient to change. Unlike the Brood X cicadas, seasonal cicadas are much more flexible to human activity in developed areas. They are not concentrated in a single 17-year generation like the Brood X cicadas. There is also a wide variety of seasonal cicada species that can adapt to a variety of habitat changes.

What else should I know?

Dr. Barnes adds there are actually three different species of the 17-year cicadas. Which species type is found in your particular area may also play a role in whether or not they emerged. While the Brood X species is the loudest and most notable, there are also 13-year cicadas that emerge in parts of Indiana.

There is also an amazing variation in seasonal cicadas. Some are green with a pattern of brown on their backs. Others are red. Dr. Barnes recommends googling the cicadas found in Indonesia and India if you want to see the colors for yourself.

How can I learn more?

If you have more questions and would like to learn more, visit the Purdue Entomology website.

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