News Category: Cicadas 101
While the deformities that we will be discussing are not limited to Tibicen cicadas (as cicadas of other genera and species are also affected by deformites of one kind or another) we will only be focusing on the deformities of the cicadas that I have been able to study here in Massachusetts namely Tibicen lyricen and Tibicen canicularis.
The molting process in cicadas for some unknown reason can go horribly wrong. The reason for this has not yet been determined but there are theories that are being floated around in some entomological circles. Whether it be due to fertilizer use or infectious diseases in host plants or just simple injury. Whatever the reason, it's a definite reality for cicadas of every species and genus.
Weed Out the Bad Eggs - Genetic Impurities Theory
One of my personal theories is its nature's way of weeding out genetic impurities. That is, if a cicada fails to molt (eclose) successfully, then from a genetic standpoint, that cicada was pre-disposed to fail because of the same genetic impurities and in this way prevents it's genes from being carried on.
However, the reverse can also be said in that cicadas of the same species in a given area may not have enough clean genetic stock due to excessive in-breeding and failure in a successful molt may also be nature's way of halting in-breeding. This may be far-fetched but it has been hypothesized that most cicadas do not travel very far from their host plant and that it may be possible that cicadas from the same parent may in fact inter-breed.
After all, why is it that there is no cross-breeding between species? Tibicens of the same genus but different species often inhabit the same areas and are present during the same times of summer. Could a female Cicada of one species be attracted to the call of a male from a different species? It's been my experience that you can attract cicadas by firing up your weedwacker or lawn mower and you may attract a female cicada of any species. Can this not be true say for a female T. canicularis being attracted to the call of a T. lyricen or the reverse?
Update 3/18/2011: After the writing of this article, there is now stong evidence in the form of photographic documentation and rsearchers accounts of unusually strange male calling songs in some Tibicen species. These strange songs indicate that cicadas may in fact be hybridizing in certain areas of the United States. There is evidence to indicate there are indeed morphological variations in the same species depending upon geographic location.
Whatever the reason a small percentage of the cicadas that I have studied seem to have among them some that never successfully complete molting.
It's Purely Chemical - Internal Chemical or Enzymatic Imbalance
What is the actual mechanism involved that enables a cicada to go from a 5th instar nymph to a fully emerged adult? That is what happens internally that triggers the eclosing process? Is there some chemical or enzyme that is secreted which causes the outer nymphal skin to separate from the internal adult teneral? Maybe this chemical or enzyme does not effectively distribute itself over the internal adult cicada properly and causes the cicada to get stuck during the process.
Deformities Example 1 - Failure in the Eclose Process
The above images show the most common of the many types of deformities in cicadas. The failure to properly eclose and emerge from their nymphal shell. Most often times it is due to a wing that seems to be stuck within. Cicadas that this happens to can live for a very long time like this and all the while they continue to struggle to free themselves. If you click on the third thumbnail to the right, you can see the adult teneral outlined inside the nymphal shell. Note how the front forelegs are still trapped within. This cicada is leaning towards the left because it is stuck inside it's nymphal shell by the left wing.
Why this happens is unclear. Perhaps it is due to poor nutrition during the final instar stages of development due to overcrowding underground or again some genetic defect that causes the wings to not develop properly which marked this cicada's doom.
Even more horrific things can happen when a Cicada get's stuck during molting. In the above examples the first thumbnail shows how this Cicada is rather "pink looking". This was a particularly hot day in August when I stumbled upon this Tibicen canicularis. The reason its really pink is because it was baking in the hot sun all the while struggling to free itself. A short time later as shown in the second photo, black ants started feeding on this specimen starting with its head. Click the thumbnails for a closer look.
When Blood Is Involved
A Cicada may struggle so hard to free itself from its nymphal shell when it's stuck that it may actually "rip" something internally that may cause it to start bleeding excessively. The name for an insect's blood is known as "hemolymph". Whether it be a wing bud or a leg. As shown in the image to the left, the extremely black section on the side of the nymphal shell is actually accumulated blood that is more than likely starting to coagulate which only inhibits the cicada further from freeing itself.
The blood must be sticking to the cicada teneral and acting like glue causing it to stick to the internal parts of its nymphal skin. This particular specimen was found on an old dead pine tree. You can click on the movie thumbnail to watch this specimen struggle in it's attempt to free itself.
So Close and Yet So Far
The thumbnail to the left is a brief movie clip that shows a cicada that almost successfully completed molting but unfortunately, it was trapped within it's nymphal skin via it's left hindwing. This specimen looked like it just needed to get a better "foothold" for leverage in order to free itself so I tried to offer it some help with the use of my index finger but unfortunately, it didn't work out. This specimen was found on an Ash tree in the cemetery where I had previously found several other deformed cicadas. This particular Ash tree was diseased and at the time of this little movie (2004) was dying. I went back to this tree this year (2005) and it was completely dead no leaves were present on this tree. I had talked to the grounds keeper in depth about this particular tree last year because of my curiosity about the deformed cicadas. He stated that it would be lucky if he got an additional three years of life out of this tree but alas, apparently last year was its last year of life.
Here is another example of a female Tibicen canicularis still bound to its nymphal shell via the hind wing. If you look at the enlarged picture, you can see some black areas on the nymphal shell. This again is coagulating and drying hemolymph. This specimen struggled fiercely to free herself and it caused the normal wing on the right to develop in the wrong position. This specimen will not make it.
Successful Molt but with Dyer Consequences
Some cicadas do successfully molt but at a very high price. They literally rip themselves from their nymphal skins, leaving various parts of themselves behind.
One of the very first Tibicen lyricen specimens that I came upon during the 2004 Cicada season was this male specimen pictured to the left. From this angle, this specimen looked rather normal to me with the exception of the left wing. It was obvious that it wasn't finished expanding its wings and that it would just take some time. However, after waiting for about an hour, I noticed that there was no difference in the shape and that it wasn't expanding.
Looking at the specimen from a different angle, certain things suddenly became apparent. Its nymphal skin is an extremely dark black color. This again is indicative of something terrible happening during molting. This also looks to be dried hemolymph.
After waiting an additional hour with little to no change I decided to gently pick this specimen up. I noticed immediately that it was missing it's left front foreleg. Looking inside the exuvum, I discovered the leg still inside! This is no doubt where most of the hemolymph was coming from. As you can see in the left hand thumbnail the left front foreleg is missing. Note the black areas just behind the left eye. This is where is leg should be. What's left is nothing more than a stump and the dark area is clearly drying blood. It makes one wonder if cicadas can feel pain.