Monday, December 8, 2014

Don't Fear the Flying Scorpions

In late October I made a quick trip to the Trinity River Audubon Center and came across a wonderful insect called the scorpionfly.  I was very pressed for time so only managed to capture a single specimen, but just a few days later Professor Jeff Hughes walked into my lab with another one, giving me both a male and female to image.

The male scorpionfly.  Weird and scary looking, but totally harmless to humans.  They don't bite or sting.
Coming upon a scorpionfly for the very first time can be a bit of a surprise.  The elongated beak of the male is pretty weird looking, not to mention what appears to be a scorpion-like stinger.  But never fear - they are harmless.  In general, scorpion flies are scavengers that eat dead insects.  And the stinger is actually the male reproductive organ. (Which in a way makes it even more scary. Scorpionflies belong to the order Mecoptera.

One reason I really like scorpionflies is that they are instantly identifiable, mainly because they remind me of my favorite part of Mad Magazine - the Spy vs Spy cartoons that were drawn in the margins of the magazine's pages.

The male genital structure of the Mecopteran.

Though called scorpionflies because they look like flying scorpions, but the scorpionfly is neither a scorpion nor a fly.  Flies have two wings while this insect has four, and scorpions are arachnids with 8 legs, not 6 as seen in insects.  
Scorpion flies are harmless to humans.  Most species either prey on small insects or eat the bodies of dead insects.  The long snout allows them to feed in narrow places and on small prey.

Mecoptera is a very old order of insects, dating back to the Permian period 299 to 251 million years ago. During the Permian, scorpion flies were the most abundant and diverse insects that went through complete metamorphosis and are probably ancestral to today's dipterans (flies) and lepidopterans (moths and butterflies).

This means they survived the Permian extinction - the largest mass extinction in the history of earth which allowed the rise of the dinosaurs -and then survived the asteroid impact 65 million years ago that finished off the dinosaurs. 

Here is a head-on view of the male scorpion fly as seen in the electron microscope.  You can clearly see the small aluminum wire I used for a mount.  The insect is attached to the wire with Elmer's Wood Glue.  It sticks to the chitinous exoskeleton well. SEM image. [10 x]

The female mecopteran lacks the long beak but has a long ovipositor.
Head of the female mecopteran. SEM image. [31 x]
What could be more scary than a scorpion-stinger male genital structure?  How about a really long ovipositor with serrated edges.
Dissecting microscope image of ovipositor of female scorpionfly.

SEM image of ovipositor.  [35 x]

This is a dorsal view (top down) of the ovipositor.  The top section is smooth and the bottom segments are serrated.  SEM image. [182 x]  

Lateral view (side) of ovipositor showing the smooth top segment and one of the lower serrated segments.  You can also see the sheath  that covers the ovipositor. SEM image. [90 x]
The rather strange image is the ovipositor viewed from the tip.  It shows that the ovipositor is composed of three parts which go together to make the tube through which the egg is expelled. SEM image.
Antenna of female scorpionfly showing sensory sensilla.  SEM image.

Sensory sensilla of antenna of female mecopteran.  SEM image. [1,900 x]
While examining the wings of the female mecopteran I found a series of small hooks on the outer edge of one of the wings.
Hooks on wing of female scorpionfly.  SEM image. [30 x]
Wing hooks on edge of wing.  SEM image. [370 x]

Hooks on edge of wing.  Note the bump at apex of the curve.  SEM image. [600 x]
Now for some scorpionfly sex.

The male attracts the female by releasing pheromones from glands within the enlarged genital segment.  Before he does this he prepares a nuptual gift of a dead insect. When the female arrives she begins feeding and he grabs on to the edge of her forewing (function of those little hooks above?) and while she eats he inseminates her.  (If only it were that easy for humans.)

This is the tip of the male genital structure.  Though I could find nothing about it, the function of the sensory hairs is obvious and I wouldn't be surprised to learn that sperm is inserted via the numerous holes.  SEM image. [320 x] 
Spiracles are the respiratory openings for the insect.  

Slit-shaped spiracles on the thorax and abdomen of the female scorpionfly.  
Dissecting scope image of a thoracic spiracle. 

SEM image of a spiracle.  [140x]
SEM image of a spiracle. [750x]
I have known about scorpionflies for many years and have always enjoyed finding them, but recently the Eastfield library added a book called Planet of the Bugs by Scott Shaw on insect evolution that really opened my eyes to just how cool scorpionflies are.  If scorpionfly ancestors hadn't survived a couple of mass extinctions, we might not have flies and butterflies around today.  It is very cool to realize that these insects were buzzing around long before the dinosaurs and are still here.

Murry Gans
Eastfield College
Mesquite, TX

Carde, R. T., & Resh, V. H. (2009). Encyclopedia of insects: Previous ed.: 2002. 
Amsterdam: Elsevier?Academic Press.

Kattes, D.H. (2009). Insects of Texas: A practical guide. College Station, TX: Texas A&M.

Shaw, S. R. (2014). Planet of the bugs: Evolution and the rise of insects. Chicago, IL:
University of Chicago.

Smith, D. (2011, June 30). The permian period. Retrieved December 8, 2014, from

Triplehorn, C. A., Johnson, N. F., & Borror, D. J. (2005). Borror and DeLong's introduction 
to the study of insects. Belmont, CA: Thompson Brooks/Cole. 

All images are covered by a Creative Commons License.  They may be downloaded, used, or modified with attribution to Eastfield College, Mesquite, TX, but may not be sold.