Sunday, July 31, 2016

Closeup of Molted Cicada Exoskeleton (and More Info)

Earlier this week, I spotted a sizable empty shell of a bug, maybe a beetle, I thought. It was about an inch tall, stuck to a corner of a porch column, seemingly hugging it, about three feet above the porch. It looked like all the innards might have been cleanly sucked out, maybe consumed by parasitic larvae, leaving only exoskeleton and maybe other chitin.

For a larger, unreduced image, click here.

Not being an entomologist or gardener who might know about bugs, I wondered how to get information about the shell's former occupant and how it departed. A Google image search yielded seemingly countless, overwhelming results.

I decided to turn to LinkedIn connections, and posted a pic and update, hoping to get someone to identify the item. I was in luck! Two people, John Rothgeb, and Steven Schwartzman, replied with great leadoff info.

From John, a declaration and web link: "Looks like cicadas or even a Giant cicada -". The website images and first .wav file sent me off to Googling more info.

From Steve, a strongly specific term and also two links to blog articles he had written about cicadas himself:
The thing in your picture appears to be the exuviae of a cicada. That word is a Latin plural that entomologists use for the exoskeleton that an insect casts off as it grows from one stage into the next.

Here are a couple of instances from my blog:
A third LinkedIn connection declared the shell to be cicada. (Happily, LinkedIn networking can be fruitful for topics besides work, careers, and occupations. (My LinkedIn home page shows more number of views for the exoskeleton picture and inquiry than any other topic I've announced in recent memory.)

Besides increasing my curiosity about the animal, the terminology I was encountering sent me hunting down definitions and pronunciations for chitin and exuviae. Interestingly, the first "c" in cicada, according to both and, is pronounced as an "s". I've heard people pronounce it as only a "ch" sound. And I myself pronounce it as "ch". BTW, those two dictionaries also provide long/short vowel pronunciation options of "i", and the first "a".

I have listed some links about cicadas, many of them YouTube videos that show cicadas molting.
Anyway, the bottom line about the clinging bug shell on the porch column: It's a castoff exoskeleton after a cicada molts and flies away, not shell remains after parasitic larva(e) dined on the insect. Coincidentally enough, a wasp that captures a cockroach for its larva's future food supply uses similar methodology as a wasp that targets cicada.

From "10 Facts about Cicada Killer Wasps"
  1. The adult female wasp will paralyze the cicada with her venomous sting.
  2. The wasp will carry the cicada to a burrow, where it will place the cicada.
  3. The wasp will lay an egg under the left or right second leg of the cicada.
  4. The egg hatches, and the larvae begins to eat the cicada, while taking care to keep it alive.
  5. Once the larvae [sic] has had its fill, it spins a cocoon, in which it will change into an adult wasp.
Such behavior looks similar to that of jewel-wasp-on-cockroach, in comparing information in "How a Wasp Turns Cockroaches into Zombies" of Scientific American.
venom compounds work fast, paralyzing the cockroach …
leads her victim to its final resting place …
Once inside her burrow, she attaches one egg to the cockroach's leg, then seals her offspring and the roach in.…
wasp larva hatches from its egg, its meal is ready to eat. And soon enough after that, a new wasp emerges from the burrow, leaving the roach carcass behind.
Note: The SA article states that the larva hatches and emerges as a wasp, omitting the details of how the larva becomes a wasp. The site explains that the stage between larva and wasp is pupa, "usually enclosed in a cocoon or protective covering".

Cicada articles:


Woody Lemcke said...

Thanks Wanda! Very detailed and interesting info on childhood memories of Galveston county.

whildtkwriter said...

YW! I'll be posting another article & set of pix prolly next month. Spotted another shell on same column, about a foot higher. Some shots I snapped showed a wasp perched on the head, some showed wasp(s) within a couple of inches.

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