The Acorn Weevil, the Creature Designer, and an SEM

I just received a very kind e-mail from an unusual source.  Lars Grant-West is an illustrator and creature designer, as well as a professor at the Rhode Island School of Design.  Is that cool, or what!  He was prepping for his Creature Design class, which is currently focusing on arthropod limbs, when he found my blog. 
 
Today's blog post is for Lars and his students.

A few weeks ago I asked Jeff Hughes, one of the biology professors here at Eastfield, to be on the lookout for "snout beetles" while he was in the field.  Jeff is a good guy and he collected some "snout beetles" for me, but not the ones I expected.   He brought in some acorn beetles.  Acorn beetles are actually very common - I had just never come across them before. According to the Texas A&M University AgriLife Extension website "Acorns of live oaks in urban areas of North Central Texas are sometimes 100 percent infested by larvae of acorn weevils."

https://insects.tamu.edu/fieldguide/bimg200.html

Once I began imaging them, I realized that this was one of the must unusual and beautiful insects I had come across.  (Yes - I am a nerd.)

Take a look and see what you think.

(All of the color images below were taken on the Leica digital dissecting microscope.)

This is my new favorite insect and this is my new favorite image.  My students say this looks like the guy from the movie Despicable Me.  Note that this little fellow is covered with bright yellow scales.

Here you can see the weevil attached to the side of a Petri dish.  The easiest way to imagesmall, live insecs is inside of a new plastic Petri dish - they have a limit area in which to move around and the plastic doesn't seem to affect the image.

That beak!!  The mouth parts are at the very tip and are used to burrow into acorns.  The weevil sucks out some of the nutrients in the acorn through its tubular snout for a meal and then lays an egg inside the acorn.  It seals off the hole with its poop.  How is that for parental care!

Notice that the elbowed antennae don't come off of the head, but off the snout.  If  you have a long snout and need to find juicy acorns to eat, I guess those antenna need to be closer to the action.

In this image the weevil is hanging upside down to the top of the Petri dish.  Note the delicate articulated antennae.

A closer look at the antennae.

In this image the weevil is walking upside down on the top of the Petri dish.  Notice the yellow, brush-like structures on each foot.  These are setae which provide lots of surface are for sticking to surfaces - a very common solution in biology.

Here is a close-up view of the setae on the foot pads of the weevil.  The trick here is to have enough total surface area to be able to stick to a surface, but to also be able to release the foot for walking.  Evolution at its best.

Now let's move on to the scanning electron microscope for a closer look.  (Unfortunately, one of my students made some changes on the way images are saved which meant I lost the usual scale bar on the bottom of these electromicrographs.  I was able to recover the magnifications and added it to each image.)

Hello there.  Note the numerous scales.  The structures under the snout are antennae.  [32x]

 

I am obsessed.  I love this image. [85x]

Now if you would just look to the left for this next shot.  [75x]

Eyebrows?  65x

The ommatidia of the eye.  [994x]

A side view of one of the feet of the weevil.  [30x]

 

A close look at the setae on the foot pad.  You can see two different types - needle-like setae on the margin of the pad and spatula-shaped setae in the center.  Also notice that the setae appear to be in groups - this actually increases their ability to stick to surfaces. 

Gorb S, Beutel R, Votsch W, et al. Structural Design and Biomechanics of Friction-Based Releasable Attachment Devices in Insects. Integrative & Comparative Biology [serial online]. December 2002;42(6):1127.

 

The tips of the antennae [65x]

This is the joint where the antennae are attached to the snout.  Looks like a ball and socket joint which should allow for lots of movement. [65x]

The tip of the snout.  Notice the lovely little pollen grain just above and left of center.  These are the jaws of the insect.  [230x]

A top down (dorsal) view of the insect.  In this image you can see how the insect is mounted in the SEM.  Wood glue!!
[14x]

This is the point where the thorax of the insect meets the abdomen.  The head would be at the top of this image.  This guys is covered with scales.  [75x]

Scales at 150x.

The elytra that cover the wings - dorsal view. [32x]




In this image you are looking at the underside of the insect and can see the ball-and-socket attachment of the legs to the body.  [32x]

A closer look a the leg-body attachment.  Also notice the small canal or hole.  My guess this is for hearing - but that is just a guess.  I will have to find out.  [150x]

 

The Acorn Weevil is my new, favorite insect and I hope an inspiration for Creature Designers everywhere.

As always, all images are under a Creative Common License.  Feel free to download, upload, use and abuse - just give Eastfield College as the source of the image.

Murry Gans