Caterpillar of the day: Therinia transversaria

It has been a while since I have had a solid post dedicated to caterpillar eyespots. I have now returned from by research trip to Costa Rica, but I will try to keep sharing its beautiful diversity through the photos and videos that I captured while I was there. The last caterpillar I observed on my final official day of caterpillar data collection was quite an exciting specimen. I was particularly excited because this caterpillar exhibited some interesting body posture changes upon my simulated attacks (i.e., light pinching with forceps).

Therinia transversaria (Saturniidae)

The photo above shows the typical resting position of this caterpillar (at least in this instar). Very cryptic, with dashes of brown that cross the body and break up its outline - a strategy known as "disruptive colouration". Note also that the caterpillar folds its body in such a way that the brown on the anterior end seems to line up with the brown on the central part of the body. This seems to be a good example of a special form of disruptive colouration termed "coincident disruptive colouration" where crypsis is increased through preventing detection of revealing body parts by visually joining them with other parts of the animal's body.

Interestingly, similar colour patterns in caterpillars caught the attention of Edward Bagnall Poulton who was one of the early evolutionary biologists / naturalists to take a close look at animal coulouration and ponder its function. His book "The colours of animals: their meaning and use, especially considered in the case of insects" published in 1890 remains a highly regarded (and cited) work on animal colour patterns and their function. For a great synthesis on disruptive coloutarion and its various functions see Martin Stevens and Sami Merilaita's recent paper on the subject:

Stevens, M. and Merilaita, S. (2009) Defining disruptive coloration and distinguishing its functions.Philos Trans R Soc Lond B Biol Sci. 364: 481-488

Once the caterpillar realizes that it has been discovered it reveals its previously hidden eyespots:

When attacked, the caterpillar pulls in its head and puffs out the body segments that have eyespots:

This is very similar to the behavour I observed in Papilio canadensis caterpillars upon attack and the behaviour apparently observed in many caterpillars with eyespots, including Sphingidae caterpillars from the genus Xylophanes  (e.g. X. tersa).

A Saturniidae bee mimic?

More Saturniidae moths were posed around my light tonight and one looked to be a different species within the genus Automeris. I poked it to see if its eyespot display differed from the other Automeris species I have seen (and poked). To my surprise it didn't reveal eyespots, nor did it fly away. Instead, it raised its wings up behind its back and fully displayed its yellow body with a black stripe. See photos below:

Before:

Post-poke:

To me it [vaguely] resembles a bumble bee. I have never heard of this behaviour or defensive strategy in Saturniidae moths, but it is incredibly interesting. Bees are common models in mimicry systems - especially in mimetic flies (e.g. Syriphidae). By resembling bees or wasps (sometimes relatively poorly) mimetic flies avoid persecution by birds so there is no reason to think that a similar strategy wouldn't work for these moths. Please leave a comment if you have any information about this species or thoughts of the defense mechanism !

I didn't get a look to see if it also has eyespots hidden in the wings. This would be interesting to know, because so many Saturniidae moths have eyespots. It is possible that this one does too and just doesn't use them. It would be interesting to know whether this species evolved from an ancestor that used the eyespot-defence. IF so then it raises some interesting questions:

· What conditions made individuals with the bee mimic defence better than ancestors with eyespots?

· Why don't more Saturniidae moths use a similar defence?

Heliconious PWND!!!!!!!!1

During my time here in Costa Rica I have slowly come to love the butterflies from the genus Heliconius. Quite a beautiful genus with distinct elongate wings that are black and marked with a splash of orange, pink or blue. Their colour pattern is a signal to bird predators that they are unpalatable. In some species this is an honest signal indicating that the butterfly is truly unpalatable, but other species are mimics. Henry Walter Bates was very interested in Heliconidae butterflies. In his book The Naturalist on the River Amazons he discusses Heliconius butterflies at some length (click here to have a read). Also, Bates' classic manuscript was focused on Heliconidae: Contributions to an insect fauna of the Amazon Valley : Lepidoptera : Heliconidae.

Today while searching for caterpillars I found a spider nomming a Heliconius genus butterfly. The spider was surprisingly small to have taken down such a large prey item. Not sure yet on the species involved and suggestions are welcome! Here are some photos of the action:

Heliconius sp. (Nymphalidae) caught by a spider

I'm not yet sure whether this Heliconius is an aposematic or mimetic species. I suspect that the chemical defence (and colourful warning signals) of Heliconius are directed towards birds, so for this spider it probably doesn't matter either way. It seems many insect species that are unpalatable to birds are fully palatable to invertebrate predators.

Eyespots and the amazing Macrocilix maia

I am continually astonished by anti-predator defences in insects. One day it might be an insect that is so well camouflaged that you struggle to find only even when you are literally inches away. The next day it could be an astonishing mimic like a fly that mimics a bumble bee. Of course eyespots have their own appeal; conspicuous circular markings that resemble eyes, usually in direct contrast with the rest of the animal's body which is amazingly well camouflaged. Eyespots with an anti-predator function have been described in fish, birds, amphibians, and of course insects. Some of the best known examples come from Lepidoptera (butterflies & moths).

Today I found some beautiful adult moths from the genus Automeris (Saturniidae). When threatened they have the interesting behaviour of spreading their forewings and revealing otherwise-hidden eyespots. To get a sense of what this behaviour I gently prodded a few. The moths spread their wings and showed off their eyespots, sometimes in doing so they fell to the ground. Even as they fell, and upon landing, they held those wings open. After roughly 2-3 minutes the wings slowly returned to their natural "tent" resting position. Subsequent prods sometimes would elicit the behaviour again, but usually initiated an escape flight response instead. This is what they look like:

Recently there has been discussion over a new and unique type of colouration on the wings of an adult Lepidopteran. The descriptions of this species from Boneo and Malaysia are borderline unbelievable.  I have to say that I was skeptical (to say the least) when I heard the descriptions. If you look hard enough at something you can often see amazing things that arn't really there.

Without tainting your view by telling you what other people see have a look at some of these photos of the moth Macrocilix maia:

 http://www.flickr.com/photos/allanlee/3506113435/

http://www.flickr.com/search/?q=macrocilix+maia&w=all&s=int&referer_searched=1

When you see the photo it really is amazing. The accompanying descriptions are just as interesting. Right now there is rampant speculation on exactly what these colour patterns are supposed to resemble. Jerry Coyne has a great blog post on it here. Read the comments below his post to see some interesting ideas.

Some are suggesting that it could be a phenomenon new to biology: mimicry of an entire scene. Currently, my view is that this is a form of masquerade: a moth that with descrete, high-contrasting markings that seem to vaguely resemble flies buzzing around a piece of feces/rotting flesh. This probably protects the moth by causing the predator to misclassify it as an inedible object(s). It seems possible that a predator big enough not to be interested in eating little flies should pass over it, but anything small enough to want a fly might not be able to subdue a big moth.

Some preliminary questions are left in my mind though:

• Wouldn't this moth have to rest on a white background for this to work, and where are these white backgrounds?
• There are flies and discrete piles of decaying crap elsewhere, why don't we see similar adaptations elsewhere?
• Does the moth move its wings to simulate buzzing flies?

As always, your thoughts and comments are welcome below, just click the "comments" link below this (or any other) post to leave a message.