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!

Photo from US: Insect Identification

cicada

Yes! This week, the title “Insect Identification” is really an accurate title. One of our own, Chris Flis, took this awesome photo out at the HMNS paleological dig site in Seymour, Texas, where our team is working hard to uncover new bones and fossils. This is our first insect submittal and I’m very excited because this is one incredible insect.
This is an insect that you rarely see, but find traces of them everywhere. During the warm months of the year, people all over the country come accross peculiar shells which look like bugs, but appear to be empty. As a kid, I would find these all over my grandparents heavily wooded backyard and I loved to scare my brother and sister with them. I would call them, along with about 99.9% of the population, locust shells. It was not until I studied insects in college that I discovered that locusts are a kind of grasshopper, and these shells I was seeing everywhere belonged to a bizarre little bug called a cicada. In this photograph, you can see the actual adult cicada clinging to its old shell, or exoskeleton. It is probably waiting for it’s new skin to completely harden so it can roam the forest in search of a mate.

Cicadas are insects belonging to the order Homoptera, an order containing mostly plant pests such as aphids, scale insects, mealybugs, and whiteflies. Cicadas themselves do very little damage to plants and are not considered pests. They have simple or gradual metamorphosis, meaning they have only three different life stages: egg, nymph, adult. The nymphs spend their time underground sucking fluids from roots of trees. When it is time for them to become an adult, they tunnel their way out of the earth, attach themselves to the bark or branch of a tree, and molt for the final time. The adult that emerges looks almost identical to the nymph, only larger with big beautiful wings. This always happens at night, so we don’t see the adult, just the skin they leave behind which is perfectly preserved and very crunchy. The adult males are capable of producing sound from their abdomen which they use to track down a mate. Cicadas are active during the daytime, so that VERY loud hissing sound you hear during the hottest hours of the day are lonely male cicadas. At night, we are serenaded by nocturnal crickets, katydids, and of course, frogs. There are around 3000 species of cicada, each producing a unique sound. You can click here to listen to some different cicada songs as well as some katydids and crickets. Most cicadas have a pretty long lifespan, remaining underground as a nymph anywhere from one to three years. These are known as annual cicadas and can be seen every year. This one in Chris’s picture is an annual cicada.

Now why do I say these are such incredible insects? You may have heard of a periodical cicada. These cicadas belong to the genus Magicicada which contains only seven species. There are two types of periodical cicadas; 13 year and 17 year cicadas. This means that these guys spend either 13 or 17 years as a nymph, underground sucking on roots, which is incredible. Not only do they live for an unbelieveble amount of time, their emergences are synchronized, creating one of natures greatest phenomenons. When an emergence takes place, millions of cicadas come out of the ground for several weeks providing food for hundreds of species of birds, mammals, reptiles, and other arthropods. These animals feast on cicadas until their bellies are about to pop, but they don’t even put a dent in the cicada population. So many of them die that the forest floor is covered by several inches of decomposing cicada bodies, giving the trees a tremendous dose of fertilizer that can only come from such an incredible event. This spectacle of nature can be seen in my favorite program ever, the Planet Earth series (the Seasonal Forests episode). These periodical cicadas look much different from the usual annual cicadas. They have a black body, red eyes, and orange veins in their wings. This website has a lot of great information about periodical cicadas, including an emergence chart which shows when certain broods will emerge next.

Thanks so much for sending in this picture Chris, it spurred such an interesting topic. I hope I’ve cleared up ya’lls misconceptions about cicadas and I hope you find them as amazing as I do.

Adult Cicada

Creative Commons License photo credit: trekkyandy
A Periodical Cicada