Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Sunday, February 19, 2012

Contortionist Caterpillars

I saw several amazingly shaped Caterpillars near the Avon Dam several days ago.
Caterpillar - what is it doing, and which end is which?
There were two of them on a small bush of  the Large-leafed Hop Bush (Dodonaea triquetra).
Large-leafed Hop Bush (Dodonaea triquetra)
As I first saw it. Dodonaea stem being stripped by Caterpillar
This is the same shot, cropped so you can start to figure out which end is which.
The head end is on the left, for that's where the leaf was being chewed.
Close-up of Caterpillar at work stripping the leaf.
The full contortionist pose

This pose is the full defensive pose. 
There is an orange protrusion in the middle of the back.
The prolegs (lumps on the abdomen which assist in grasping the stem)
have protective spines.
The real legs are beneath the head end, and are protruding 
to the right of the image.
They look like weapons.
There are 3 pairs - (the insect's normal quota of six legs ***)
There is some visual distortion because of the diagonal angle of the shot.
Click on image to see in full detail.

Caterpillar head (on right) curled back, tail probe extended.

Caterpillar in first defensive pose - head raised (at left)

Caterpillar in second defensive pose (head reflexed)
Now I need to confess that I found it difficult to "visualise the parts of the caterpillar" in its upside down position, so the preceding three images have been inverted.
This is MY limitation, not the Caterpillar's, for it functions perfectly well with its head low down.
But I don't, so I felt it easier to "understand" what was what, by inverting those images.
But for the sake of honesty, I ought show the caterpillar feeding in its normal position
So here it is "the way it was".
Actual position of Caterpillar - the way it was seen (pose 1)
Actual position of Caterpillar - the way it was seen (pose 2)
OK.Now to the challenging bit - finding out what I had seen.
Of course I went straight to the wonderful Australian Lepidoptera site, run by Don Herbison-Evans and Stella Crossley. In fact I went to the page dealing with Caterpillars of Australian Moths

The reason I did that turned out to be the undoing of my search for an ID as well.

I have seen lots of Hawk Moths in my time, and in seeking to ID them, I have looked at many web pages for these moths. I knew therefore, that most have Caterpillars which have a prominent "horn" on their tail end.
And that's what I thought I had here.
Hawk Moths are in the Sphingidae family.
I went there and looked in vain for a match to my Caterpillars.
I knew they were distinctive, so surely somebody must know.
I emailed Don Herbison-Evans who promptly replied the next morning, that I had found caterpillars of  Neola semiaurata.
Sure enough, they have a perfect match for my caterpillars.

I wish to express my appreciation to Don for his assistance, and also for having been largely instrumental in creating the amazing website which is such a valuable resource for people like me, who keep finding moths to be of interest.

OK, that's the ID, but what is it about the strange shape?

Neola semiaurata is in the Notodontidae family.
I had not thought to look in that family, for my caterpillars.
The page for this family says: Many Caterpillars of this family adopt a characteristic posture when they feel threatened: they raise the tail and the head to make a U shape. (Yes)
Many of the species of NOTODONTIDAE have Caterpillars with reduced anal prolegs and several humps on their backs (yes) Some are hairy and some are smooth except for a few spines and fleshy tubercles. (Yes)

The large flat area at the tail end of my Caterpillars are in fact the last pair of "prolegs" which have become modified into serving in a display function, it seems (to me). That is the last bit of the caterpillar on the right hand side of the image above. The red "spike" is not hard tissue. It looks pointy, but is in fact soft tissue, which is capable of being everted, when the caterpillar is in the display role.

The plants on which my Caterpillars were feeding are in the Sapindaceae family. Many plants in that family are contain mildly toxic saponins with soap-like qualities in either the foliage and/or the seeds, or roots. Many of the Caterpillars in this Notodontid family have larvae capable of producing chemical defences (cyanic acid, formic acid, and other ketones not commonly found in other Lepidoptera.

So the plants are likely to be strong chemical producers, and the Caterpillars themselves may contain, or even produce toxic or noxious chemicals. So, there might just be something to back up all that scary defensive posturing. 

It worked well enough to prevent me from touching the caterpillars. I have been stung by Cup Moths previously, and I still remember how sharply that sting hurt me. I wasn't about to take any chances with these caterpillars.

OK, I think we have just about done the Caterpillar story.
What does it become after metamorphosis?
What kind of moth, I mean, and what does it look like?
Once again the specific website says: "The adult moth is rather dull compared to its Caterpillar, having forewings speckled dark grey, and pale orange hind wings. It has a wingspan of about 6 cms". There is a photo of the pinned specimen of an adult moth on that site.

Compared to the spectacular caterpillars, the moths of Neola semiaurata are somewhat disappointing.

*** I referred above to "the insect's normal quota of six legs"
It ain't that simple folks. See this page on "prolegs".
Caterpillars and many other larvae of insects, such as Wasps and Sawflies have developed "prolegs".
These can function like legs, but lack the hard tips typical of true legs (see my images above where the "prolegs" are holding the Caterpillar onto the stem, and the real legs are raised in a defensive posture.

Now for the tricky bit.
There are variations away from the standard, so, while all Caterpillars have six true legs, many caterpillars have up to 5 sets (10 in total) prolegs. These are soft tissue organs, used for walking and clinging on to stems (as in the case of my Caterpillars). These prolegs have a set of microscopic hooks on the base (crochets). The last pair of prolegs are adapted as "claspers".

Then the variations really set in.
The Australian Lepidoptera site says: "The Caterpillars of some species have atrophied prolegs, and appear to only have 8, 6, or 4 prolegs, or even no legs at all. In the metamorphosis, all the prolegs disappear".

It gets even worse, folks.
In the adult phase, in many species of Butterflies, one pair of true legs may disappear. Many butterfly species have only four legs. The Wanderer Butterfly is one such example.

So, where does that leave our understanding that "Insects have six legs"?
Out the window, I suggest.
Well, with the vast majority of  species, and genera and families of insects, it is accurate. But there is no such thing as a "safe" hard and fast rule.

Once again, thanks to Don Herbison-Evans for the information which is the source of most of that discussion on prolegs and real legs.


Wilma said...

quite an amazing creature!

Denis Wilson said...

Thanks Wilma
Yes, so amazing, I really still do not understand quite how and why it has developed that hammer-shaped rear end.
One must do a lot of "defensive posturing" to have developed such an elaborate body transformation.
Clearly designed to keep birds and small animals at bay.
Well, it kept me at bay too.
I am kicking myself that I didn't get a "face on" view of its mouth and eyes. But in truth, I didn't know which end was which when I fist saw it.
Not often one says that.

Snail said...

That's one of the weirdest things I've seen in a long time, Denis. You keep coming up with the goods.

It's quite a bit like the caterpillar of the lobster moth, which is in the same family. Strange animals.

Denis Wilson said...

Hi Bronwen
You get the prize for the best comment this year.
I also browsed Wikipedia before I wrote my article, and came across the mysterious Lobster Moth caterpillar.
Too weird.
I think there must be something to do with the chemicals these animals ingest.
A bit like the Wanderer Butterflies being toxic from their caterpillars living off the Milk Vine family.
In this case the Sapindaceae is not "used" much in Australia, but very many tropical fruit plants come from them, and some drugs are sourced from this Family.

Anonymous said...

Thanks for your website as I also found those caterpillars today on a form of acacia plant and your site enabled me to find out what they are. It was interesting watching them curl back and the 'eye' open.

Denis Wilson said...

Hi Amanda
Glad to have been able to help you identify these remarkable Caterpillars.
Thanks for letting me know - the Feedback is nice for me, personally.
Makes late nights on the computer worthwhile.