Thursday, February 15, 2018

Spotted Oleander Caterpillars... Fifth Instar moving on to Sixth Instar and... IT IS HAPPENING!

The time is growing near.  An inevitable change (a metamorphosis) will happen soon.  Twenty six days old.  Fifth instars.  Three have molted and are sixth instars and one is in process.

Empyreuma affinis.  Spotted Oleander Caterpillars.  The babies.  Our babies.

                                                        Spotted beauties.

Each with their own personality.  This one had a bit of a tail feather issue after the last molt.  Cute.

For the most part they spend their days eating and pooping and growing.  But they are different in their own ways. 

You are familiar with number nine who has developed quite the personality of wandering and getting himself into trouble despite his miniscule size (he's finally made it to 5/8 of an inch!).  Then there is number eight (smaller than the others yet larger than number nine x2).  Booger is a wanderer and can often be found traversing the edge of the top of the box or, on especially ambitious days, sitting on the table beside it basking in the sun and celebrating his freedom!  Big Boy is the largest and rarely picks his head up from the leaves.  Long John is the second largest in girth but the longest when he does a full stretch having reached an inch and a half in length.  Mr. C has a bit of a back-door issue and some trouble with frass elimination often walking around with one hanging out of his rear.  And while the rest of the gang just let their frass fall where it may, Mr. Neat has perfected the ability to grab it with is anal prolegs, chuck it off to the side and keep his area neat and tidy.   The last two Nicole calls the quiet twins.  They are about medium in size and maintain a pretty low profile.

As our little ones have continued to grow the macro photography of them has become a tad easier.  We have been able to start to more easily identify their 'parts' and to learn more about them.

In this shot, for example, you can see the Stemmata which are six pairs of simple eyes.  They look like an upside down smile.  Caterpillars cannot really 'see'.  Their stemmata detect changes in light intensity (because they are composed of photoreceptors or light-sensitive cells), but they cannot form an image.  Also, that 'spike' hanging down from his chin is most likely a shot of the spinneret where its silk glands are located.

In this shot you can see the cats segmented antennae.  There is one on each side just under the eyes (most obvious on the right side of the photo here).   Instead of using their eyes to find food, the caterpillar relies on its antennae.

A pretty decent view of the spinneret (hair sticking off of the chin) and the Maxillary Palps (projection at junction of spinneret with chin) which are sensory organs that direct food into the mouth as well as the segmented antennae.

Caterpillars do breath.  Spiracles are their breathing pores.  They are usually located one on the thorax and eight on the abdomen.   We've tried to highlight (with black arrow) what we think are the spiracles on our cats but they are hard to see.

One of the easiest cats to see this on is the Canna Leafroller.  The white dots are the spiracles, the webs coming off of them are the tracheae.  Also easy to see on this transparent caterpillar is the Dorsal Vessel (the dark line down the center of the back).  Instead of hearts, caterpillars (and other insects) have this vessel separated by valves called ostia.  Hemolymph gathers in the valves and is pumped from the abdomen toward the head.  The hemolymph continues to flow down through the rest of the body, until it gathers back in the chambers, repeating the process.  Hemolymph does not carry oxygen as blood does but instead carries nutrients and immune cells.

Another interesting feature on our cats is their feet.  The front (thoracic legs) seen in the above photo are jointed with hooks and are used to hold onto food.

Their abdominal and anal prolegs on the other hand have crochets (or small grasping hooks) that let them climb very well.

Nicole does not like to use the camera flash around the caterpillars very often but found a good opportunity the other day as one was molting because it seemed the stemmata were covered and therefore the bright light may not affect the little one too much.  This allowed for the great shot above of the prolegs  and a few others.

Freshly molted and preparing to fluff the hairdo.

And now it is time to do the cute little wiggle dance.



Yum.  Nothing like a mouthful of some freshly molted exoskeleton and hair!

While the others just keep on growing, we still have no idea what is going on with Number Nine.

Number Nine continues to attack the easier (top layers) of the leaves but will succeed at the whole leaf after others have had a go.  Lately he seems to be losing his spots.  Perhaps it is because he just molted although the others obtain brighter spots upon molting.  So, the mystery continues with this one.

Speaking of molting here is a recent shot that clearly shows the old head capsule coming off as the light shines through it.

Even the thoracic legs are show to be coming out of the old exoskeleton (hence the light shining through their tips).

To continue... the caterpillars increased size means that their molts are also easier to photograph.

A fresh and complete exoskeleton of Empyreuma affinis - the Spotted Oleander Caterpillar.

The head capsule shots are below.  For reference the head capsule is smaller than the head of a straight pin.

Rear Shot - You can clearly see the two sides (the left and right vertex) and the Coronal Sulcus (joint down the middle).  Those little hairs are called Setae.  They are very sensitive to touch and can also be irritating to predators.

The underside shows the mandible and other previously mentioned parts.

In this front shot you can easily view the Stemmata (eyes) and the Adfrontal Sulcus and Area (triangular section) and the Frontoclypeus (section just below the triangle).

Since we've focused so much on molting it is probably worth mentioning again that three of the babies are now sixth instars.  For a few days we were not sure if that meant they would soon be pupating (beginning their metamorphosis) or not.  Well, this morning, the answer was confirmed for at least one of the little ones.  As Nicole was carefully removing the cover on their home she noticed one in the upper corner had webbed itself in with silk.

Can you see the fine covering of sliken hairs?

Since caterpillars can be very vulnerable in this state and should not be disturbed Nicole has tried to leave him alone while still doing her best to monitor the situation.  Throughout the day more of his black body hairs have begun to leave his body and fill the web around him.  Eventually, all of them will come off and cover him.

Both a happy and sad situation ... for at least one of our little ones, THE METAMORPHOSIS HAS BEGUN!