In My New Skin

Yao Ming
Creative Commons License photo credit: Keith Allison
Yao Ming –
The guy just didnt stop growing.

I bet you’ve never thought of growth in as much detail as I have. As an Entomologist, I think about it a lot! It’s very simple for vertebrates. You eat, drink and sleep - and your body grows. Do you tell your body to grow? Do you try to grow? No, it just happens, slowly at times and quickly at other times. Sometimes we grow up and unfortunately, sometimes we grow out! The point is that it is an involuntary action that our body undergoes, just like breathing, blinking, salivating and blood pumping! I am so grateful to be a human and have this happen effortlessly and without many bumps along the way.  Arthropods, on the other hand, got the short end of the stick! Arthropods have to go through a serious ordeal to get from one size to another, known as molting or more scientifically, ecdysis.

Insects and other arthropods are not like us, obviously! Whereas we have an endoskeleton, or skeleton that supports our body from the inside, they have an exoskeleton, or a hard shell covering the outside of their bodies. This exoskeleton functions much in the same way as ours does. It supports the arthropod, as well as acting as a point for muscle attachment. Additionally, it protects them from certain predators and parasites and helps to keep terrestrial arthropods from desiccating or drying out. It also contains certain sensory structures that are very important to insects and their many relatives.

Exoskeletons are formed by a long chain polymer called chitin. This compound is very tough and resilient and is also found in other animal structures such as the beaks of octopi and squid. When I’m teaching kids about exoskeletons, I like to compare it to a suit of shining armor that a knight would wear. Now, if it was a young knight, he would have to grow, so he could not always wear the same suit of armor. He would have to trade it in for a new, larger one. This is the case with arthropods and their exoskeleton. In order to grow and get larger, they must shed their exoskeleton and grow a new one.

This is where things get a bit hairy! In order to shed their exoskeleton, arthropods have to go through a scientific process called ecdysis. I’ll spare you the boring scientific details, but basically, they excrete a liquid that separates their old skin from their bodies. This process is called apolysis. They then form a new skin. They excrete another chemical which digests the innermost layers of the old skin and they crawl out of what’s left. What’s left behind turns into a dry crunchy empty shell. Shortly before this process, arthropods stop eating, start swelling up a bit, and eventually stop moving or being able to function at all. If anything at all goes wrong during this process, they are finished!

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Creative Commons License photo credit: emills1
A katydid nymph molting,
getting a little help from a friend!

Many insects have to hang upside down and let gravity help pull them out of their old exoskeletons. If they fall from their perch before they are done, they will not be able to get everything out and will either die or be severely deformed. To make matters worse, they are super defenseless during and after this process, making them prime targets for predators! If an arthropod is able to successfully complete their molt, they are stuck with this brand new, super soft exoskeleton. They can neither walk nor fly. They are completely vulnerable for at least a couple of hours. Have you ever eaten soft shell crab? Well, it’s not some cool different species of crab you’re eating, it’s just a regular crab that has been harvested right after molting. They cook it while it is still soft, so you’re eating the whole crab, shell and all. I can’t ever bring myself to eat them, it kind of grosses me out! The most commonly used crab for this, in the United States, is blue crab.

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Creative Commons License photo credit: emills1
A deformed katydid due to a failed molt

If the arthropod is able to successfully remove all body parts and limbs from the old skeleton and find a safe place to rest until their new skeleton hardens, they can go on living their little bug lives, until the next time they have to molt! This process gets even more complicated in insects that have what we call complete metamorphosis, such as butterflies, beetles, flies and bees. Insects like grasshoppers, cockroaches and praying mantises go through incomplete metamorphosis, so every time they molt, they have relatively little changes in their bodies. They mainly get bigger and some grow wings. As we all know, a butterfly starts out as a caterpillar, it gets bigger as it molts, but when it’s time for it to pupate or form a chrysalis, the process of molting involves the insect changing its body completely. This makes it even MORE of a challenge for them.  It’s very interesting to note that similar chemicals that digest the insect’s old exoskeleton, digest most of the actual cells of the larva, leaving only some cells alive. These remaining cells reform the organism into a completely different looking organism, like the adult butterfly!

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Creative Commons License photo credit: emills1
The Exuvia of a Giant Prickly Stick,
a walking stick from Australia.

The cast away skin of an arthropod is called the exuvia or exuvium. When it’s first removed from the animal, it’s soft, like the new skin, but as it dries out, it becomes very crunchy!

I bet almost everyone has seen one of these. You know those empty insect shells you can sometimes find stuck on trees? I grew up calling them locust shells and I used to love scaring my siblings and friends with them. Then I’d get a lot of pleasure out of crumbling them up! Well, they are not locust shells; locusts are a type of grasshopper. These exuviae belong to cicadas.

Tibicen Cicada
Creative Commons License photo credit: jasonb42882
A cicada molting.

Cicadas are those funny looking insects you hardly ever see but always hear in the summer. You can hear the rattling noise they make during the hottest hours of the day. The immature cicadas can spend anywhere from 2 to 17 years feeding on tree roots underground, depending on the species. They emerge at night, start climbing a tree, and complete their final molt to adulthood on the way up. The next day we find the shells, but the actual cicadas are high up in the tree tops by then!

Every arthropod on the planet has to go through metamorphosis that involves molting. Insects, spiders, centipedes, millipedes and crustaceans. Interestingly, millipedes are born with only a few segments and legs. Each time they molt, they add another segment and 4 more legs.  I could go on and on about the amazing molting process. The point is, next time you are getting down about anything in your life, think about how easy we have it compared to the bugs of the world. Be thankful that we have easy access to resources we need to survive, we have no real predators and we don’t have to molt! The whole process terrifies me really, so I’m very thankful!

Until next time, happy bug watching!

Ghosts in the Trees

Last night, I was reminded of how unusual some of the insects we raise here in the Cockrell Butterfly Center are to most people. I had set up a table in the grand hallway of the museum to promote our outreach program, cleverly titled “Bugs on Wheels.” As soon as I left the Butterfly Center’s doors, I had drawn a crowd that didn’t seem to subside for the entire evening!

I think what grabs most people’s attention are our exotic walking sticks, which we have been displaying for several years. As soon as people see our giant prickly stick, they commence with “what on earth is that?” type of comments, and I love to educate them!

Walking sticks belong to the insect order Phasmatodea or Phasmida. This name comes from the Latin word phasma, which means ghost. It refers to their amazing camouflage skills, which in the right setting, can make them vanish right before your eyes! These insects are all herbivorous and harmless, having no venom or large mandibles for biting. This makes them an easy target for insectivores! So they have come up with some pretty fantastic ways to protect themselves from predators. These insects have simple metamorphosis, so the immature nymphs, look like tiny versions of the adult. Here at the butterfly center, we raise 5 different species of exotic walking sticks. I’d like to share a little about each one with y’all!

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Creative Commons License photo credit: emills1 
an immature female

The Giant Prickly Stick, or Extatasoma tiaratum, is one that really draws the crowds! The females are very large, 6 to 8 inches in length, and very fat! They range in color from light peach to dark red-orange. They are often – almost all the time, actually - mistaken for a scorpion. This is no accident, this species is native to Australia, the venom-capital of the world! They spend their entire lifetime hanging in eucalyptus trees feeding on the yummy foliage and easily folding themselves to resemble a dried up leaf.

If they are spotted by a potential predator, they will curl their abdomen to look remarkably like a scorpion. This warns predators that if they don’t want a nasty sting, they should stay far away. What a clever defense! Since they are, of course, completely harmless. They have a very soft exoskeleton which keeps them confined to the safety of the tree tops. If they need to do anything like lay an egg, they drop it to the leaf-covered ground. The females have small vestigial wings, but are incapable of flight. They can lay up to 1,000 eggs in their lifetime and can live a little over a year. The males are quite a bit smaller, very thin, and excellent fliers. They are equipped with much longer antennae than the female, which they use to sniff out a mate.

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Creative Commons License photo credit: emills1
Spiny Devil

The Spiny Devil (Eurycantha calcarata), is a close neighbor of the prickly stick; they are native to New Guinea. These adorable stick insects have very different habits. They are equipped with a very hard exoskeleton that is covered in hard spines, especially the legs! Since they are a harder egg to crack, they are not as attractive to eager insect-eaters, plus, they put up quite a fight! They can use their legs as a weapon by squeezing with all of their strength. I can speak from experience and say, it hurts!

When threatened, they can put on quite a show, raising their abdomen and back legs. We like to call it “the handstand of pain!” Since the female has the freedom of reaching the ground, she uses the pointy tip of her abdomen (her ovipositor) to lay her eggs deep in the soil. The male and female look quite similar, both are wingless and they are nearly equal in size. Both sexes can live for about a year and a half as adults – not bad! The male does have one distinguishing characteristic, a single very large spine on his hind femur.

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Creative Commons License photo credit:
emills1 Ouch!

They are very territorial and use this spine for fighting. They can seriously injure or even kill another male during combat. Still want to mess with these guys? Well, the males can also emit a very foul chemical that smells just like a skunk. However, they are usually pretty laid back.

The Phyllium celebicum or moving leaf insect is a breath of fresh air. These leaf mimics are petite, dainty, have no spines or smells, and are 100 percent cute! They inhabit the rain forests of Malaysia.

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Creative Commons License photo credit: emills1

Since they have no other defense mechanisms, their camouflage has to be absolutely perfect, and well, see for yourself! They also spend their entire lives in the canopy, dropping their eggs to the ground haphazardly. The female, pictured right, has larger wings than the Giant Prickly Stick, but their only function is camouflage. The male is half the size of the female and he’s an amazing flyer! These live a little under a year and we love to have them around.

I actually noticed something very interesting from observing them. The outer 1/2 inch of the female’s body is only a layer of skin, and all of the organs are arranged down the very middle of the abdomen. This is important because I started seeing a couple of them missing chunks of their abdomen, but they didn’t appear to be injured. I’m sure they get nibbled on by several herbivores in the wild - it’s a pretty cool adaptation.

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Creative Commons License photo credit: emills1

Sharing the same rain forest is the Giant Jungle Nymph (Heteropteryx dilatata). They are spectacular, very large and beautiful. The females are bright green and usually 7 inches in length with a wide abdomen. They have small wings which they rub against their bodies to produce a hissing noise. Their thorax, abdomen, and legs have rows of sharp spines. When disturbed they thrash around violently and they also do “the handstand of pain.”

They spend most of their time in the trees and only travel to the ground to lay their eggs. The male is brown and only about 4 inches long. They have bright crimson hind wings and are very showy. They are always very nervous and thrash around a lot! This species is harder than the others to raise. They need high humidity and they take a long time to develop.

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Creative Commons License photo credit: emills1
a male

The eggs take around 17 months to hatch and the nymphs take over a year to develop into adults. This species can be very aggressive, but we always end up with a few that can be handled, they are very curious and active. 

The last resident of southeast Asia is the Annam stick insect (Baculum extradentatum). These look very similar to our native walking sticks. They are very slender and really resemble a twig. These are interesting little creatures. When disturbed, they will essentially go limp and flop to the ground. It’s really the only option for them since they are so defenseless.

The most interesting thing about this species is that they can be completely parthenogenic. This means that the females can reproduce without males. We do have males in our populations and it is a full time job making sure we don’t have too many individuals. They are egg-laying machines. Their life span is about a year and males and females look very similar, but the males are much smaller.

These walking sticks are some of the most amazing insects I’ve worked with. I’m so impressed with their diversity and beauty. Next time you see them in the Entomology Hall or in the Grand Hall, come by and see them, you’ll certainly be amazed!

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Creative Commons License photo credit: emills1
male
Baculum





Science Doesn’t Sleep (8.27.08)

MEC's green roof among others
Creative Commons License photo credit: 416style

So here’s what went down after you logged off.

There’s a reason that cowboys don’t make good anthropologists – and it has to do with Hobbits.

It’s aliiiiiiive! A green roof can reduce your heating bills and protect your waterproofing – plus, it’s pretty! Check out a how-to here.

Some ancient documents are taking their message high-tech: the Israel Antiquities Authority is putting all of the Dead Sea Scrolls – all 15,000 fragments – online.

Construction in London has unearthed thousands of human skeletons – and the oldest are soon going on display.

Recently developed: a wheelchair that walks for you by means of a “robotic exo-skeleton.” Check out the video here.

How fast can we go? Usain Bolt’s astonishing, record-setting Olympic races have forced scientists to reconsider.