Walking Sticks and Other Camouflaged Insects

Walking Sticks and Other Camouflaged Insects
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It’s a jungle out there.  Entomology professor Julie Peterson says there’s an estimated 10 quintillion insects on earth’s globe.  If you have not heard of that number before, let’s just say that insects have the largest biomass of earth-bound animals, and probably represent 80 percent of the classes on the planet.  And there are still more species that have not yet been described. An article in The New York Times predicted 300 pounds of insect for every pound of human!

What’s interesting to many though, is an insect’s ability to go about undetected as a form of protection or in order to stalk his own prey.  Being truly cloaked through camouflage, mimesis or using mimicry, means that animals can hide in plain sight.

Camouflage by Nature

We know that reptiles, such as iguana, can change their body shape, texture, color and markings.  Birds use their camouflage in marked feathers to blend in with grasses or to protect themselves when resting, nesting or stalking prey.  Marine animals like octopus and squid can change color by contracting muscles that pump pigment to their skin’s surface and they can color-match the seafloor or blend into a reef.

Insects can be highly camouflaged as well.  There is an owl butterfly that no matter which way he looks—right-side up or upside down—doesn’t blend into the background however, but confronts with two menacing eyeballs that would ward off any lesser-than-brave predator who is leery of the great horned owl.  This particular deception telegraphs to birds, back off!

Whether the stealth tactic is to use coloration, found materials, anatomy or behavior to achieve disguise, entomologists refer to this as crypsis, forms of camouflage that make the insect difficult to distinguish against a particular background.

A Bug’s Figure

The standard insect body has three parts: each segment had bendable appendages that stick out called jointed appendages. The whole body then is wrapped in a skeleton on the outside, called an exoskeleton, that gives it shape, dimension, and a crunchy skin.

Sometimes young insects look like adults only smaller.  They would be growing up under an incomplete metamorphosis and would be called nymphs.  If the insect changed from one form, say from a larva or egg into another shape like a lightning bug, they would go through complete metamorphosis.

A great disguise and a unique metamorphosis are found in the walking stick (Bacteria virgea).  A walking stick looks like a home craft project where someone glued leaves and twigs to one another to form a long-legged stick-figure of a bug.  This insect has pulled out all the stops when it comes to deception. They often sit or even dangle among foliage and during the day move very little, often remaining motionless.  Some exhibit enigmatic behavior such as swaying side to side, as if imitating the breeze such as would be seen on actual twigs on a windy day. If startled, most walking sticks will freeze or go lifeless, dropping and blending in with the forest floor.  As if that were not enough deterrent for its predators, some have a repugnant gland with which they can exude a noxious chemical spray and potentially induce blindness in its foe. In addition, as a safety measure for their young, the eggs of stick and leaf insects are remarkable in that they actually resemble seeds of particular plants.

Chasing Dinner

It takes a lot of energy to hunt and chase prey.  Certain bugs have a camouflage feature that can trick food into coming to them.  For example, there is one insect, a loner of sorts, that mimics a very pretty pink and purple flower.  If, for example, a fly was to swoop in to sample the flower’s nectar they will instead get eaten by the hungry Malaysian orchid mantis (Hymenopus coronatus).  In set-up, this mantis has found they have the best luck when they situate themselves in flower-rich areas in order to complete the deception fully.

In the caves of New Zealand is a glowworm that produces clear sticky threads that they dangle from the ceiling similar to a spider web.  The larvae glow and, of course, other insects are drawn to the light, get tangled in the thread, and become dinner. This is a huge tourist draw in New Zealand as seven caves are advertising this starry night adventure and there is a YouTube feature that captures this perfectly (See: reference).

The Assassin and the Leaf

There is a bug called the Stenolemus bituberus, the assassin bug that can navigate a spider web without getting stuck.  They often time their movements to the wind so the spider will not feel the web jiggling but can lure them in by plucking the threads, feigning helplessness, and thereby stab the spider with their snouts.  Another species of the assassin bug, Acanthaspis petax,

 typically eats ants and then glues ant exoskeletons on their back as a form of disguise.  It not only looks weird—some stick twenty or more carcasses on their backs—but they also smell like the creatures they wear thus allowing them to infiltrate an ant colony and eat at will.

Looking Like Nature

Butterflies, moths and katydids widely exhibit leaf mimesis—a nature-created mimic, as their forewings are broadened to resemble the shape of a leaf, which can be green to brown, looking fresh or dried.  There is a type of katydid that actually has a strong fold line running the length of the wing to appear like the midrib of a leaf. Others may sport scalloped wings or appear as if some herbivore, (an animal that feeds on plants), has taken a bite from the leaf!  To further confuse predators, when the leaf insect walks, it rocks back and forth and for all intents and purposes, looks like a leaf being blustered about by the wind.

Reference:
Arnosky, Jim. Hidden Wildlife: How Animals Hide in Plain Sight. New York: Sterling, 2017. Book.

Engel, Michael S. Natural Histories: Innumerable Insects: The Story of the Most Diverse and Myriad Animals on Earth. New York: Sterling, 2018. (American Museum of Natural History), Book.

Toppen, Ph. D., Jodi Wheeler. Orchid Mantises and Other Extreme Insect Adaptations. North Mankato, MN: Capstone Press, 2015. Book.

Romm, Cari. “Insects Are Scary Because Your Brain Confuses Disgust With Fear”. The Cut.

Glowworms in Motion—A Time Lapse of NZ’s Glowworm Caves

Numbers of Insects (Species and Individuals) Smithsonian. (Including pages of individual bugs and their sizes.)

Natural History Museum. Spotlight: the Owl Butterfly

Orchid Mantis. Current Biology

Ripley’s Believe It or Not!

Smithsonian on YouTube for the assassin bug

Why Bugs are Not Huge. Live Science
Image courtesy of Pixabay.com