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!

katydid 012

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.

Feb2010 069

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!

Feb2010 084

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!

Meet Charro, our new resident iguana!

The Butterfly Center recently acquired a new iguana.  His name is Charro (which means “cowboy” – as in “charro beans”) and we believe he is between 5 and 10 years old.  For the time being, he is housed in a cage in the rainforest area.  We may eventually let him loose to wander freely in the Center, once he is thoroughly acclimated – but for now, he seems to be content (and is particularly visible to patrons) in his cage.  Keeping him confined does allow us to find him easily in order to take him outside for some exercise and sunshine on a daily basis. 

We’ve had several free-ranging iguanas in the Center over the years.  It is a perfect place for them – much better than the situations in which pet iguanas are typically found.  Indeed, all of our resident iguanas have been pets that outgrew the space and/or time their owners could provide them.  I think it is unfortunate that these creatures continue to be sold as pets:  what starts as a cute little green lizard ends up as a small dinosaur – and most people are not prepared to handle the latter.

But as a result of all the iguanas we’ve had, I’ve learned more about them than I ever expected to know.  They are actually very interesting and personable creatures!  If you’d like to learn more yourself, read on – or check out the excellent information at the website of the Green Iguana Society.

iguana of sea
Galapagos Island Iguana
Creative Commons License photo credit: Ansgar Berhorn

Iguanas are in the same family (Iguanidae) as the little green or brown anole lizards we see in our gardens here in the southern USA.  The most common species available through the pet trade is the common or green iguana.  Green iguanas (the scientific name is Iguana iguana) are common in tropical areas from Mexico to South America.  In their native habitat, they often sit sunning themselves high up in trees, especially along rivers.  If a hawk or eagle flies over (both are major predators of iguanas) they will fling themselves into the river below.  They are excellent swimmers!   There are several other species of iguana, including the spiny or black iguana (also common in Central America, especially near the coast), and of course the famous marine iguanas and land iguanas of the Galapagos Islands (both species believed to have evolved from green iguanas). 

summer-09-042Baby iguanas are about 8 inches or so long and bright green.  But they soon get much larger, some growing to over 6 feet long.  As they mature, they lose their bright green color, and males in particular gain “secondary sexual characteristics.”  People often ask about Charro’s large jowls (the big lumps on either side of his head).  We like to say that they are like biceps on men – enticing to females and intimidating to other males!  The jowls, large dewlap (flap of skin below the chin), and the orangish skin color are all characters seen in mature male iguanas.  Male iguanas also develop fatty deposits on top of their head.  Mature females are slimmer and duller colored, with smaller jowls and dewlap and no head lumps. 

Although much less colorful than the babies, adult iguanas can change color up to a point.  We’ve noticed that Charro gets darker when he is taken out into the sunshine, and lighter when he’s back in his cage.  Iguanas use their color to regulate their body temperature – they darken up to absorb more heat.  An iguana’s color can also indicate its mood or stress levels (sometimes their colors become more contrasting when threatened or frightened).  Male iguanas in particular become more colorful when they are in their breeding season.  The orange becomes brighter, and the black stripes on the tail, etc., more pronounced.

Iguanas apparently have excellent vision, and can see colors as well as we do.  They also have a “third eye” (called the parietal eye), a clear scale on the top of their head.  This organ senses light and dark, and alerts them to aerial predators.  

Male iguanas in particular develop pointed “tubercular scales” on the back of the neck, and have a ridge of flexible spines along the back.  I have not been able to find any known function for these, beyond ornament.  Quite a few of Charro’s ridge spines have been broken off, and we are not sure whether they will grow back.  Iguanas do molt their skin periodically – unlike snakes, which shed their entire skin at once, iguanas lose theirs in patches over several weeks. 

Iguanas can live for over 15 years, but usually don’t make it that long in the wild because other animals (including humans) love to eat them!  In fact, they are sometimes called “chicken of the trees” or “bamboo chicken.” Their eggs are also eaten, and their skin is sometimes used for belts or boots, etc.

summer-09-040Iguanas themselves are strict vegetarians, which is rather unusual among lizards (most eat insects or other small animals).  For us, of course, it is fortunate that iguanas have no interest in eating butterflies!  We feed Charro healthy salads of vegetables and fruits.  Greeny leafy vegetables such as collard greens are especially good for him.   According to the Green Iguana Society website, although iguanas will eat almost anything you offer them, they should not be given any animal protein!

Because iguanas, especially the males, are quite territorial, we have been advised (by none less than the director of the Houston Zoo) to keep only one iguana at a time.  Indeed, many years ago when we had a male and female, they had a tremendous battle and the male was badly injured.  Although in nature you may see several iguanas in close proximity, they are not social creatures and really only get together to mate. 

Long-time patrons of the Butterfly Center will remember some of our previous iguanas.  Sidney died in 2004 at the age of 14, after more than three years in the Center.  A large, stocky and colorful iguana, he acted more like a dog than a lizard; he was so friendly that he would crawl into people’s laps to be petted.  When Sidney died, we had an autopsy done; the vet told us he died of a heart attack (apparently a common cause of death in older, captive, male iguanas!) 

Gandalf was not quite as friendly as Sidney, but was a truly magnificent specimen.  Unlike Sidney and Charro, he had a complete, unbroken tail that was exceedingly long (Gandalf was about 6 feet long including the tail.)  Unfortunately, after several years of climbing all over the Center, he made an unfortunate misstep.  We believe he slipped off one of the planters on the second floor and crashed onto the cement floor around the cenote.   This undoubtedly happens in nature as well: during one field season in Costa Rica I used to admire a large iguana that sunned himself every day on a high and slender branch of a cecropia tree along the Puerto Viejo river.  One day I noticed that the branch had broken off…I never saw that particular iguana again. 

Stretch immediately preceded Charro.  He was never a happy or friendly iguana, and died of old age/ill health earlier this year (2009), less than two years after he came to us.   Charro was acquired for us earlier this summer by Olga, one of the visitor services staff who has a friend at the Brownsville Zoo, Charro’s previous home.
 
From our previous experiences we’ve learned that individual iguanas, once you get to know them, definitely have personalities!  So far Charro seems to be a very laid-back, tolerant, and well-behaved iguana.  However, we always impress upon visitors that iguanas can bite, although it is usually a last resort and they usually give plenty of warning.  However, when it happens, an iguana bite can be serious.  They have lots of very sharp little teeth – it’s like getting slashed with a hacksaw.

Fortunately, we have learned to read the signs:  iguanas typically give behavioral clues about their mood.  When an iguana is comfortable and happy (for example when we pour water over Charro’s head, something he seems to particularly enjoy) it will stand up on its front legs, raising its head in the air.  Most iguanas also enjoy being petted, particularly behind the head, or under the chin and jowls, or along the back.  Sometimes they close their eyes in pleasure, leaning into the caress just like a dog or cat, and even look as if they are smiling!

An angry iguana, however, is quite fearsome.  If frightened or seriously irritated, it will typically turn its side to whatever is bothering it and stand up on all four legs, apparently trying to maximize its size.  It may also walk forward in a stiff-legged manner, sometimes opening its mouth and wagging its tail.  This is not a friendly wag – it means the iguana may whip with its tail or even bite!  At this point it’s time to back off and give the iguana some space.

People sometimes voice concerns about iguanas and salmonella.  Yes, some iguanas can carry it.  So after handling Charro or any other reptile, for that matter, it is a good idea to wash one’s hands thoroughly, especially before eating.

summer-09-043If you don’t see Charro in the Butterfly Center when you visit, check outside by the Kugel Ball.  A number of docents have volunteered to take him out for a “sunbath” on sunny days.  Iguanas need the heat, as well as the UV A and B wavelengths provided by the sun’s rays (or the simulated sunshine provided by a UV lamp), to get warm enough to move and to eat/digest food, as well as to manufacture vitamin D (just like humans).  We try to get Charro outside for at least half an hour, several times a week.  It’s also a good way to let people see him up close!

Any of you iguana experts out there – I’d be happy to hear feedback about any aspect of iguanas and their care.  We’re always learning about them!

Science Mystery: What came out of the Bearded Dragon’s Nose?

photo credit: cbattan
 Merlin, our bearded dragon

You can pick your friends and you can pick your nose, but you can’t pick your friend’s nose. Even if your friend is a Bearded Dragon.

I have been working with reptiles for quite a while now and have seen some weird things. But one of the weirdest happened during Summer Camp. Our bearded dragon had just shed the majority of his skin except for a few pieces around his mouth. It was actually one of the campers who noticed another piece of skin protruding from the beardie’s nose. It had sand on it and we couldn’t tell if it was coming out or stuck into his nose, so we picked at it and out it popped.

It was bizarre looking, kind of stringy, and surprisingly long – just over a centimeter. As it turns out, we were a little hasty. Since our beardie wasn’t having any difficulty breathing, we could have left the nostril shed alone as it would have come out on it’s own (if you are properly caring for your dragon). Our dragon is none the worse for having “picked” his nose but we definitely won’t do that again since the sensitive linings of the nose could have been damaged.

photo credit: cbattan
 What are you looking at?

I like learning something new every day – and this definitely qualified as a new thing. So like Shel Silverstein‘s sharp-toothed snail – don’t pick anyone’s nose, you never know what’s in there.

Learn more about Bearded Dragons! Check out our posts on baby beardies born at HMNS.

Mantis Madness

Blog 097

Creative Commons License photo credit: emills1 
So tiny I almost couldn’t focus

One of my favorite parts of this job is raising baby insects. It may not be like raising a baby, or even a cat or dog, (sometimes you have to feed them living things) but it is still very fun and rewarding. Plus, baby insects are really cute as you’ve seen from my previous posts. This week, the stork brought us about 100 Giant Asian Mantis nymphs. They are so cute.

Giant Asian Mantids (Hierodula membranacea) are a species of very large, impressive mantids from Southeast Asia. They are typical-looking and resemble some of our native mantis species, but are much larger. They come in a wide range of beautiful colors, such as bright green, yellow, orange, grey, pale peach, or brown.

They are quite voracious and will go after a wide variety of prey.  The adults are of one of the few species that will even eat a pinky mouse (shudder). Mantids are known as ambush predators. This is why they have camouflage coloration, which helps them hide from their predators and prey. They are not equipped for running after prey, so they have to be able to lunge and grab things very quickly. Their characteristic “praying” front legs are equipped with lines of teeth or spines to grab and hold on to squirming animals and they are very strong. Mantids also have excellent vision.  Predators in the insect world need to have accute vision to be able to see potential prey moving and flying around them.

Violet is the proud mother of these babies. She is a gorgeous specimen, bright peach colored with light violet eyes (hence the name). She is the first mantis we’ve been able to take out for Bugs on Wheels. While others may freak out and jump, fly away, or bite your hand thinking it’s a really fat cricket, Violet just climbs up and looks around curiously. It’s like she trusts us, or, just knows that we take care of her and provide her with food. We will be so sad to see her go some day, but I feel great knowing I’m raising her babies and hopefully one of them will be as special as she is.

Blog 090

Creative Commons License photo credit: emills1 
Violet, posing for the camera

Raising baby mantids is really fun and easy, and it can be a great science experiment for home or the classroom. Mantis egg cases are available for purchase from a few web sites, like Insect Lore and Carolina Biological Supply, or some garden centers and nurseries. You can release most of the babies into your garden and keep the rest to raise yourself.

Once the babies hatch, they can be fed flightless fruit flies which are available from Fluker Farms.  They should be kept in a container with a mesh lid and plenty of small sticks and twigs. They need to have several places to hang from so they can molt. They should be fed fruit flies at least 3 times a week and sprayed with a fine mist of water a couple of times a week.

Once they get bigger, you can move on to feeding them small crickets, then bigger crickets and so on. If you have several, be sure to separate them as they get bigger, so they won’t eat each other. When they have made it to adulthood, you can release them into the wild, so they can start the cycle over again. 

Watching insects complete their life-cycle is really an amazing experience and it can teach you so much – maybe even mom and dad will learn something. I will leave you with this video of Violet’s green sister catching her meal. Happy bug watching.
If you can see this, then you might need a Flash Player upgrade or you need to install Flash Player if it's missing. Get Flash Player from Adobe.

Learn more:
Katydid!…did she?
Big Beetle Bonanza
Vinegaroon gives birth to…grasshoppers?