You all remember the last invasion of cicadas in our area back in 2004, right? The sound was almost deafening, and when we walked in our gardens they fell in our hair, and crunched when we stepped on them on the sidewalk. Fun!
Well, that batch was Brood X, a really big batch, which in the cicada world are called "broods". There are at least 15 broods of periodical cicadas, some of which emerge every 17 years, while others every 13 years.
And now they're back, with Brood II of the 17-year cicada ready to emerge from the ground here on the East Coast, which they typically do when the soil temperature reaches 64 degrees. They'll leave the ground, crawl up tree trunks, and emerge as adults from the shell of the nymph. (Watch!) You know, like a butterfly coming out of a cocoon.
After those 17 years of hibernating they'll live about 2-4 weeks, without eating a thing. Their only mission now is to mate.
Effect on Plants
Cicadas perform a service for host trees by aerating the soil when they emerge, though the total effect on the trees depends on the tree. Cicadas split small tree branches to insert the eggs. The branch will usually wilt, die and fall off the tree. The cicadas then emerge from the branches and enter the soil. For large trees it's no problem - just a form of natural pruning. This process CAN cause damage to young trees, especially fruit trees and dogwoods. If you have young trees that might be damaged, cover them with bird netting when you first notice the cicadas.
Effect on Critters, including Humans
They don't bite and yes, they may fall on your head. But have you considered eating them? Some people do, out of curiosity or for shock value. People in many Asian countries have eaten cicadas for centuries, and there are records of Native Americans eating cicadas. Descriptions of the taste range from comparisons to asparagus to popcorn to shrimp. Yum.
Other animals sure love eating them, including deer, squirrels, birds, and dogs.
In order to attract females, male cicadas emit a deafening chorus, which can reach 90 decibels -- as loud as a lawnmower. They also buzz when they're alarmed (as demonstrated in this short video).
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