"Albino" Bugs

I am frequently presented with descriptions or images of what people assume are “albino” insects. Usually, the specimens are clearly lacking pigment. The mistake is understandable, but there is precious little information widely available to explain what is actually going on. Allow me.

As far as I am aware, there is no such thing as an albino insect, spider, or other arthropod. Aside from some species endemic to caves where there is no sunlight, there are no species permanently devoid of pigment. What people are finding are specimens that have recently molted. In the immediate aftermath of shedding its exoskeleton (“skin”), an insect is generally soft, wet, and white, eventually hardening, drying, and darkening. The newly-minted adult American Cockroach shown above is a typical example. Note the slightly darker individual at bottom that had molted hours earlier.

Molting is known as ecdysis in scientific lexicon. It is a highly complicated process that is governed largely by hormones, and makes possible the astonishing transformations known as metamorphosis.

We came to learn of the complexities of insect development through the diligent work of physiologists that commenced around the early 1920s. Some rather primitive and grotesque experiments by Stefan Kopec in Poland demonstrated that just prior to molting the insect brain sends a signal to the prothoracic gland which in turn produces molting hormones called “ecdysones.”

Ecdysones are actually steroidal hormones. Their levels are elevated suddenly before molting, triggering a cessation of feeding and stimulating gene expression (and/or suppression?) that will apply to the next stage of development.

Many freshly-molted true bugs are pink

The presence of another hormone called “juvenile hormone” means that the next developmental stage will be another larval or nymphal instar. The absence of juvenile hormone (JH) in the haemolymph (insect blood) signals transition to the pupa or adult stage, whichever applies. JH is also important in reproductive biology in the adult male insect, even though its effects are dormant during metamorphosis.

Back to the actual process of molting. Epidermal cells begin manufacturing a new exoskeleton, while at the same time enzymes are liberated into a “molting fluid” that erodes the inner layers of the old cuticle, making those amino acids and sugars available for recycling into the new exoskeleton. Muscle attachments to the old cuticle are actually broken through rhythmic contractions of the insect’s body from back to front.

Cicada molting to adulthood

The old cuticle splits along predetermined ecdysial sutures, kind of like the perforations that allow you to easily open a box. As the insect extricates itself from the old exoskeleton, a waterproofing substance is deposited atop the new cuticle. This material is secreted by dermal glands.

Once the insect is free of the old “skin,” it takes in air to literally inflate itself to a larger size while the new cuticle hardens. This hardening process takes hours if not days, and is called “sclerotization.” This process begins prior to molting in the jaws (and sometimes other body parts like the crochets on the prolegs of caterpillars).

Insect larvae have a thinner, more flexible exoskeleton than nymphs, pupae, and adult insects. Therefore they are often not as densely pigmented. The shed exoskeleton of a larva with chewing mouthparts is often consumed by the insect itself so as to recycle the nutrients and eliminate evidence of its presence to keen-eyed birds and other predators that are alert to such signs of insects.

People who find the shed exoskeletons of insects may think that the ghostly objects are actually living specimens. The durability of shed exoskeletons is indeed astounding. Cicada shells may remain affixed to trees and other vertical objects for months after the adult insect has lived and died. Oh, and those stringy white things protruding from the seam where the insect emerged? Those would be the remains of major tracheae. Yep, even the tracheae of insects is sclerotized.

A shed exoskeleton is called an "exuvia," plural "exuviae"

Considering how vulnerable insects are during, and immediately after, molting, it is amazing how many survive to adulthood. Predators can get them while they are soft and immobile. They can become hopelessly entangled. Yet, here they are, the most successful and abundant of all organisms.

Sources: Hadley, Debbie. 2013. “How Insects Grow – The Molting Process,” About.com.
Mills, Erin. 2011. “In My New Skin,” Beyond Bones blog, Houston Museum of Natural Science
Resh, Vincent H. and Ring T. Cardé (Eds). 2003. Encyclopedia of Insects. San Diego, CA: Academic Press (Elsevier Science). 1266 pp.

Time to Delete "Moth" From Our Vocabulary

I recently learned of a controversial theory of metamorphosis that got me thinking about moths and butterflies. More on that later. Perhaps National Moth Week also had something to do with my thought process, and/or a Facebook post by a friend purporting a difference between moths and butterflies. Folks, there is no such thing as a difference between moths and butterflies.

There is no difference between moths and butterflies that does not have exceptions:

• Moths have feathery antennae. This is a myth. A few do, the males’ more “feathery” than the females’, the better to detect her pheromones wafting on the winds. Most moths have filamentous (hair-like) antennae.
  
• Moths are active at night. Hogwash. Most species are nocturnal, but there are plenty that fly during the day. Many fly both day and night. There are some butterflies that are nocturnal for that matter. I have personally seen some hairstreak butterflies attracted to lights at night.
  
• Moth caterpillars spin cocoons. Hardly any moth caterpillars spin cocoons, actually. Most simply have a naked pupa (the term “chrysalis” could also apply), often underground, sometimes inside a gallery the caterpillar bored in dead wood or living stem, stalk, or root. A cocoon does help insulate a pupa in exposed situations during weather extremes, so some species add this silken covering.
  
• Moths eat clothing. There is so much wrong with that statement I’m not sure where to begin. The larvae (caterpillars) of some moths do consume dried animal products like wool garments and blankets, but they are in an extreme minority. The feeding habits of the vast majority of moth caterpillars are of no consequence to people whatsoever.

It is that last item that hints at the real reason we insist on an artificial distinction between moths and butterflies. We need a villain, and the moth is it. Butterflies can do no wrong! They are colorful and carefree and their larvae eat weeds we don’t like. Moths are evil, their caterpillars consuming our crops and ravaging our forests. Moths are black, brown, or gray, and hide themselves in shame by day, only daring to emerge under the cloak of darkness that is night.

Moth Week may have started to peck away a little at the mythology of moths, but we should consider banishing the term “moth” from our lexicon altogether. Science recognizes that weevils, “ladybugs,” and “fireflies” are all types of beetles. Mosquitoes, gnats, and no-see-ums are acknowledged as types of flies. Moths are butterflies, by virtue of the fact that they are in the same order: Lepidoptera.

The theory of metamorphosis that made it onto National Public Radio implies that it isn’t butterflies and moths that are different, but the adult stage and the caterpillar stage. So different are they that perhaps they are separate species merged into one being. The caterpillar leads an entirely different lifestyle than the adult, and “dies” during the pupal stage, only to be “resurrected” as a new, winged creature at the conclusion of the life cycle. Yes, the majority of the scientific community scoffs at this idea, perhaps rightly so, but one can argue that the similarities between adult butterflies and moths are much smaller than the differences between the larva and adult of any one species.

Moths need positive attention for many, many reasons:

• Scores of moth species are endangered, or have populations that truly border on unsustainable. Contrast that with the “sky is falling” cries from butterfly conservationists every time there is the slightest slump in populations of hibernating Monarch butterflies.
  
• Moths are true pollinators, while butterflies (and many moths, to be fair) are merely “flower visitors.” Female yucca moths (family Prodoxidae) intentionally stuff a wad of pollen into the stigma of the host plant, thereby fertilizing it. The moth does this because her caterpillars require viable yucca seeds on which to feed. The caterpillars rarely consume the entire seed set, and both host and herbivore prosper. Several tropical orchid species rely solely on certain sphinx moths for pollination.
  
• Moths are incredibly important to the food chain. Countless birds, bats, even grizzly bears, rely on moths as a food source. Oh, add fish, reptiles, amphibians, spiders, and other insects to that list. Many of those predators are in fact moth specialists. Some spiders even mimic the pheromones of certain female moths to attract the male moths to their webs.

It is time to call “moths” what they really are: butterflies. Time to stop discriminating based on assumptions, myths, and preconceived notions of what moths should be. Reality is far more subtle, and nature lacks the anthrocentric lens we view Her through. Our vocabulary should reflect that reality, and not our prejudice, cynicism, and biases. Who is with me?

Hatched!

Remember the “Carpet Cocoon” story I did back in March, and the one on the “Carpet Caterpillar,” too? Well, the story has come full circle now.

Sometime last night, an adult moth emerged from the pupa that the caterpillar formed in the yogurt cup I had it in. I remember thinking that I needed to put a paper towel or tissue around the inside of the smooth cup so the moth could climb up and fully expand its wings for a successful molt. Naturally, I had the lid off the cup, covering a small, live beetle on my drafting table last night….So, this is what I found this morning:

An empty cup, with a now empty pupal case (and caterpillar head capsule at the left). No moth to be seen anywhere. Terrific. I looked high and low, and finally, by sheer luck, discovered the surprisingly large, perfectly healthy moth tucked neatly in the door jamb of the front door, at about ankle level. It had managed to eclose (the scientific term for emerging as an adult insect from a pupa) perfectly, in the most imperfect circumstance, with no further intervention from me. Astounding.

The comments I received on my initial post about the caterpillar were mostly directed to my assertion that the moth was nothing much to behold. I only had images from BugGuide.net to go by, and I was not impressed. Suffice it to say that seeing the living creature has changed my opinion. It seems to have actually transformed the carpet fibers into the shimmering scales on its wings.

I had errands to run today and was in and out of my apartment frequently. On the last, late afternoon return home, the moth flew out the door. Ah, freedom! Well-deserved, too, I might add.

Cicada shells

Almost every summer I receive several questions about strange bugs sitting motionless on fence posts, tree trunks, and other upright objects. I thought I would do an entry here to explain the mystery.

The descriptions of the creature that people give to me vary from a “cross between a crayfish and a beetle,” to “gnome-like,” and all mention the large claws on the “front end.” No one has ever seen anything like it, and it is no wonder. Normally, the creature they are seeing lives fairly deep underground.

I have taken to calling these bugs “former insects,” since the objects being seen are not entire insects but the cast exoskeletons (“skins”) of cicadas, family Cicadidae. Scientists call these shed skins “exuviae,” all that remains behind when the insect molts from the nymph stage into an adult. Dragonflies, damselflies, stoneflies, and mayflies also leave behind these ghostly but tangible shadows of their former selves.

The average person rarely sees an animated version of a cicada nymph because the mature nymphs emerge from the soil at night, climbing the nearest vertical surface, and then splitting the exoskeleton down the middle of the back to allow the escape of the wet, soft adult under the cover of darkness. The fresh, pale adults are extremely vulnerable, but their principle predators are diurnal, so they avoid instant death by coming out at night. Cicadas are large insects, so they can be quite conspicuous under the best of cryptic circumstances.

An adult "annual" cicada, Neotibicen sp.

Most people in eastern North America see the shells of “annual” or “dog day” cicadas in the genus Tibicen. They then hear the loud “songs” of the adult male cicadas, not often seeing the insect that makes such a racket. Despite the name, annual cicadas still take a long time to grow up. They live a subterranean existence as nymphs, sucking the sap from tree roots for at least five to seven years. The generations are staggered, though, so some adults emerge every summer. This is in contrast to the synchronous broods (populations) of the periodical cicads or “17-year locusts” that emerge en masse in the late spring or early summer every 13 or 17 years, depending on the latitude of the population.

I like to get questions about things like cicada exuviae. It shows that people are observant and curious, two qualities I really admire in my own species