To me, fireflies are the quintessential early summer insect. Late summer however is dominated by a larger and very noisy bug that is hard to ignore.
Cicada is a Latin word meaning ‘tree cricket’. There are over 2,000 species of this insect worldwide in temperate & tropical environments. They are even considered a culinary delicacy in several countries of the world.
A cicada ‘singing’ from his perch under some leaves
There are two basic types of cicadas- the most common one we see are the annuals. Annual cicadas typically live 2 to 5 years and spend much of that time underground in a nymph stage, digging through the soil to tap tree and bush roots to suck the juice contained therein. As you can imagine, they have strong front legs for digging. Near the end of their lives, they emerge from the ground usually in July and August in Ohio, attach to an object and then molt, turning into the adult form that we are used to seeing (and hearing). They live a month or so in this final life stage. Most of their time is spent looking for a mate; females lay hundreds of eggs in tree branches. The eggs hatch and the nymphs drop to the ground and dig for cover, starting the life cycle anew.
The second type of cicadas are the periodicals, which get the most publicity. Periodical cicada nymphs emerge from the ground in Ohio usually in May and June, but they do not do this every year. There are 2 major types of periodicals, 13-year cicadas and 17-year cicadas. They emerge from the ground every 13 or 17 years respectively, though there are different broods in different geographical areas, which makes the situation a little more complicated. For instance, in the current year 2011, the Great Southern Brood (also known as Brood XIX) of 13-year cicadas have hatched in parts of 16 states from North Carolina to Missouri.
Why do periodical cicadas emerge every 13 or 17 years in different areas? Chances are that this is a strategy to deal with predators- a predator with a shorter life cycle than the periodical cicada broods (which happen in prime numbered years, by the way) will not reliably be able to make this insect a regular part of its diet. However, periodical cicadas, unlike their annual cousins, emerge in great numbers in a short period of time, many millions of insects covering the landscape in their brood years. This phenomenon is known as predator satiation, a reproductive strategy by which a creature appears in huge numbers all at once, during which many are eaten by predators but many more survive simply due to the fact that its predators have eaten so many of them that they are too full to eat the others.
Ohio’s most recent experience with periodical cicadas came in 2008, when Brood XIV emerged from the ground in the southwestern part of the state.
Cicadas- particularly periodical species- can damage trees by laying their eggs in young branches, which are split open by the emerging nymphs. This is known as ‘flagging’. There are various ways to limit this damage, including pesticides, netting, and delaying the planting of young trees.
This cicada was rather absurdly perched upon a stem of grass
Cicadas are rather startling-looking bugs when you see them up close, with their large bodies, nearly transparent wings and bulging eyes. They have 5 eyes, believe it or not- 2 large prominent ones, and 3 smaller ones on the forehead in between them. But their most interesting characteristic is the very loud buzzing sound that the males make to attract a mate. Unlike crickets which rub their wings to generate sounds, cicadas use membranes in their abdomens called tymbals which are vibrated to generate sound. Chambers within the insect’s body modulate and amplify the noise. Each cicada species have their own specific ‘calls’ distinguishable by their own species. It can be quite a racket. Periodical cicadas may even coordinate such calls, perhaps to drive predators off. It would certainly drive me off!
This sound can reach a volume of up to 120 decibels, which can cause permanent hearing damage if done very near a human ear for a period of time (which luckily rarely happens- people get the heck away from that kind of close-range racket).
Unless you let one ‘sing’ on your shoulder, cicadas are harmless to humans. They don’t bite, though if they land on you they may mistake you for a tree and try to suck some sap from you- I’d recommend shooing them away 😉
The cicada’s main predator are birds. Just last week I saw a House Sparrow carrying a still-buzzing cicada in its beak as it flew over a building. Squirrels, Praying Mantises, and the apt-named Cicada-Killer Wasp also prey upon them. But judging by their numbers, I don’t think we’re going to run out of cicadas any time soon.
Here are a couple photos I took of an adult cicada newly-emerged after molting in mid-August.
Notice the sturdy front legs on the nymph body shell, designed for heavy digging
You can see the 3 small eyes on the forehead between its 2 large eyes if you look closely
The sound of cicadas and high summer go hand in hand. It’s curious to think that these insects spend most of their lives beneath the ground and then emerge for their final month of life out in the sun.