Tuesday, May 16, 2017

Periodical Cicadas Early Emergence

A Periodical Cicada perched

     So the calls and emails have all been coming in. Some people happy and fascinated, others much more fearful, as they think that a great plague is about to strike. The emergence of dozens of cicadas has many people wondering what's going on. Some are aware of Periodical Cicadas, sometimes called locust in a reference to biblical invasions of insects, others are not. 
     Indeed, we are in the midst of an emergence of Periodical Cicadas, but not the natural phenomenon of a great cicada year. The Big One is not due until 2021. Cicadas are insects known for the loud songs of the males. While we have numerous species of annual cicadas that come out every year during summer (many of which take more than one year to mature, but they're staggered in breeding so some are out every year), Periodical Cicada are much different. 
     Periodical Cicadas (Magicicada species) emerge in huge numbers in late spring, generally on 13 and 17 year cycles. There are 7 Magicicada species, of which 3 are local to the DC area. They generally time themselves so they come out in gigantic numbers, thus the reference to biblical plagues of locust and their alternate name. By all coming out (and earlier in the season before predators like Cicada Killer wasps are active) at one time in such huge numbers, they make it impossible for all of them to be eaten. Though a favorite food, they just are too many to all get eaten. Since they come out after such an extended period of years underground, no single predator has adapted to feed on them exclusively. They just overwhelm all the potential hazards, so though thousands die, millions make it. 
     Since their emergence is synchronized over different regions, people have divided these regional  cycles into Broods. There were 23 different Broods recognized at one time, but some have gone extinct. The DC area is part of Brood X. 
     Periodical Cicadas spend the vast majority of their lives underground, usually either 13 or 17 years. The larvae feed for years on the roots of trees for the most part, sucking what they need to survive from them, molting into bigger larvae every year. Though that many feeding would seem to damage the trees, they rarely cause any real damage in this stage. Eventually their internal clocks go off, usually after the ground 8 inches down reaches 64 degrees Fahrenheit. Sunnier areas thus have them emerge before shadier ones. 
     The larvae (referred to as nymphs) somehow time their climb out of their burrows for the same year (mostly). Some get to the surface before others, but many may just wait until the rest are ready and stay underground, though their burrow entrances of pushed up soil, called turrets, may become noticeable.

Exit holes and a shed skin

     Those that are ready to emerge often wait until just after dark and then climb the nearest thing around them. This is usually a tree, but tall plants and even walls are fair game. They often have better success obviously on less slick surfaces such as rough barked trees. The nymphs climb until they get some altitude and find a good place they can grasp firmly. They then undergo the final molting of their exoskeletons of their lives.

A cicada partially exiting its old skin

     The skin (exoskeleton) splits along the back and slowly a white-colored, very soft-bodied adult cicada crawls out the back. Although the initial separation from the old nymph skin may only take a few minutes (though can take much longer too), the soft adult will cling, often by its abdomen, until its legs and rest of the body hardens and darkens enough to protect and carry its weight. This usually happens by the next morning. It then joins others of its kind, eventually forming massive choruses of males calling for females. Here's a video showing a cicada undergoing its final molt: 


A cicada starts to spread its wings and dry off as it is close to completing its final molt

     After mating, the females insert their rice-like eggs into twigs, preferring ones about the thickness of a pencil. If enough cicadas lay their eggs on a sapling, it can really hurt the young tree. On older trees it often just results in pruning of smaller branches. The small branches and leaves that die off, sometimes even breaking and hanging downwards, is referred to as "flagging." The eggs hatch and the young either fall to the ground or crawl out of the fallen branches until they find some tasty tree roots to feed on, feeding like this for the next 13-17 years. Both young and to a lesser extent adults feed by sucking plant juices, which is typical of this group of insects called Hemiptera. This cycle then repeats itself. 

The damage caused by the cicada inserting its eggs into a twig.

     That's what's supposed to happen and the vast majority of the time does happen. But there are exceptions. Sometimes periodical cicadas emerge either earlier or later, up to 4 years either way. These are referred to as stragglers. This has been recorded as happening since the early 1800's, so is nothing new. 
     The speeding up of development is called acceleration. It is often connected to weather and climatic changes. So for example, multiple hot and cold weather patterns may trick some into thinking it's passed multiple years and come out early. This is what may be happening locally now. Regardless why, we are having an early emergence in some local populations throughout the DC area. 
     So it may seem as though we have tons out now, but they're a very small percentage of the overall brood. Wait until we see the true appearance of Brood X in 2021! Sometimes when enough periodical cicadas emerge earlier (and plus or minus 4 years seems to be the most commonly occurring stragglers), it is believed that new broods may start. But it would take quite a few to emerge and then somehow survive so many years to start a new brood, at least in theory.
     No matter how many emerge, Periodical Cicadas are a favorite food of just about anything. You'll see birds gorging themselves on them, and this may well lead to many more nestling survivors in these times of plenty. Squirrels and other animals that normally don't regularly eat insects may now be seen stuffing themselves and their young with this fantastic food supply. I've even seen copperhead snakes feast on them.
     And animals aren't the only ones. In many cultures, including several Native American Indian tribes, people also feed on cicadas. In some cultures their names translate to "shrimp from land." They are low in fat, high in protein, and quite nutritious. Being arthropods like shellfish, those with that sort of food allergies may want to think twice, but it's not a big deal for others. Having said that, remember that they've been eating off the roots of trees for up to 17 years and so have absorbed in some cases what the trees have been exposed to. This could be mercury or pesticides, but in most cases, they are more than safe to eat. Indeed I always eat them when they emerge in huge numbers. While better fried with butter (and much more shellfish-like), you can also just eat them raw. They are best when they're soft-shelled, white and recently transformed. Otherwise you will have the extra crunch to contend with once they harden and darken as adults. Cicadas have a nutty taste to them. If you don't believe me, try them yourself. Or perhaps you can just be satisfied watch me eat one:

Eating a 17 Year Locust back in 2004

     So what we have now are stragglers from Brood X. I for one really look forward to this fantastic natural phenomenon which is rarely observed in the world, something that reminded people of the stories of insect plagues. For me though this is just a glimpse into the wonderful world of nature for which we have to wait so many years to witness again!

My son poses with a Periodic Locust from Brood II in the mountains back in 2013

9 comments:

  1. Thanks for this educational, (to me), post. I did not know a lot of this info. But I'm going to pass on eating them for now.

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  2. Hi Alonso, great post! It may be worth mentioning that the locusts of the Biblical "plague of locusts" and the Mormons' Utah experience were actually grasshoppers that showed up in vast numbers and ate everything. Not related to our Cicadas, which as adults don't actually devour vegetation (although they will still suck juices).

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  3. Thanks for your succinct info! You answered my question - I knew some of this info but had never heard of stragglers before. Great post!

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  4. Great post! Thanks for all the valuable info, as we are newcomers to the area.

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  5. Where do we stand in the cycle? Are they affected/delayed by the cooler weather?

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  8. another great article! Thanks Alonso. So many people have been asking about these!

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