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!

Where Have All the Bugs Gone?

It’s that time of year again. The days have gotten shorter and the temperature is slowly dropping. You may have been too busy to notice, but sometime between the shopping and cooking you probably have thought to yourself: I haven’t had to swat away any mosquitoes, or I haven’t been dive-bombed by clumsy June bugs. Where have all the bugs gone? Did they die? Are they hibernating? Well, the answer isn’t quite that simple. Over the last millions of years, insects have learned to employ all sorts of strategies to ride out the winter. While we are putting on thick socks and sweaters, the bugs are right there with us. They are everywhere, right under our noses, literally!

Visitors of the Prayerful Sort
Creative Commons License photo credit:
Clearly Ambiguous

If you’re an insect, you basically have two choices; you can stay or you can leave. An overwhelming amount of insects choose to stay put and deal with the frigid temperatures. One of the best ways to deal with the cold is to suspend your growth and remain as an egg, larva (or nymph), or a pupa. The adults of these insects do die off in the winter, but they are very busy until then. In the late summer and early spring, praying mantidsall around are laying their egg cases in preparation for the winter. They will lay hundreds of eggs, glued together, attached to a stick or leaf, and cover them with a thick layer of foam. After constructing her last egg case, the mother of many will pass away. Through the winter, the egg case will remain safe until it feels the warmth of spring. Then hundreds of tiny mantids will hatch and start the life-cycle over again.

If you are like the June bug, you will spend the winter as a fat grub, lazily feeding on roots all winter deep underground, where it is much warmer. When spring arrives, they form a pupa and emerge as adults in early summer, giving rise to the name June bug. Similarly, dragonfly and mayfly nymphs will remain under the water’s surface where temperatures stay warm enough to sustain them. This is often under a thick layer of ice! There are plenty of mosquito larvae down there to feed them through the long months. Right now in Texas, swallowtail butterflies are forming a chrysalis. The life stage that usually lasts about 2 weeks, will last for 3 months or more. Many of our visitors have a hard time thinking of a chrysalis as a living thing. It doesn’t resemble anything alive at all. When they see them wiggle in response to touch, they are always amazed. The thing that they don’t realize is that aside from not being able to see, they know exactly what’s going on. They can feel the days getting shorter, and the temperature dropping. They won’t make a move to emerge until spring comes!

If an insect is stuck as an adult, the most vulnerable life stage, it gets a little trickier! As long as they can keep their body temperature above 45 degrees Fahrenheit, they will make it. In Texas, this is not a problem, but in the north, they sometimes have to use drastic measures. These insects often find shelter in hollowed out trees, in leaf litter, and under rocks or dead logs.

If this cannot keep the freezing temperatures away they can do something pretty interesting. They can lower the water content in their bodies and replace it with a substance called glycerol. This chemical has several practical uses, but most importantly it lowers the freezing point in their bodies, acting as antifreeze! This is what can make an insect that appears frozen and dead to magically come back to life when thawed. That’s pretty impressive! This, along with going into a hibernation-like state called diapause keeps them alive. One insect that uses this method is the mourning cloak butterfly. This beautiful butterfly is the first to come out of hiding and appear in the spring.

Now if you’re a social insect, you pretty much have it made. Honeybees can store several pounds of honey for food. They don’t even need to leave the hive which is kept warm by the body heat of all the bees. Ant colonies spend all year building up a food supply and stay very deep below the ground. Even some insects that are not social will seek out others to pile on top of for warmth, like ladybugs.

bugs 2
Creative Commons License photo credit: Jef Poskanzer

Butterfly in HDR
Creative Commons License photo credit: chefranden

There are some insects that have opted to take a yearly vacation to sunny Mexico, which would definitely be my choice! The monarch, perhaps the most well known insect in North America makes this amazing journey every year. It’s a mind boggling to think that millions of butterflies fly up to 3000 miles to a few sites that they have never been to or seen before, how do they know how to get there? It is a mystery that keeps us all enchanted by the amazing insect. If you’d like to learn more about the monarch butterfly and their journey, visit the monarch watch website.

Since we live in an area with very mild winters, there are some bugs that we still see all year, including a lot of butterflies. There are a few local monarchs that don’t feel the need to migrate south. Every year we get several calls from people who have spotted a monarch and want to know what will happen to it or if they should help it. The answer we give them is to just let it be, the temperature will probably not drop low enough to kill it and if it does freeze, the butterfly will find shelter. They know how to deal with the cold! So you may enjoy this little break from the bugs buzzing all around us. As for myself, I can’t wait until the spring when all of the bugs are back, happily doing their jobs to keep the world turning! Plus I hate cold weather!

Go buggy! Learn more about insects:
The Sphinx Moth: It’s a Work of Art
Don’t worry, it doesn’t hurt: learn how to pin a butterfly
Do butterflies breed? Your butterfly questions answered