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Make Like a Scorpion, and Other Arachnid Designs

Arachnids (a class of invertebrate arthropods, most with six pairs of appendages, of which four are usually for locomotion) make up some of the scariest creepy-crawlies to most people. The class includes spiders, daddy-longlegs, mites, ticks, scorpions, and horseshoe crabs. They have simple eyes, unlike the compound eyes of most insects. Also different from insects, arachnids have a fused head and thorax (the cephalothorax) and abdomen; the cephalothorax is often covered by a hard carapace. 

The first pair of appendages in spiders, the pedipalps, help hold prey; in scorpions, they act as pincers. Lacking jaws, spiders suck the juice out of their prey and discard the exoskeleton. Some hunting spiders have exceptional vision, with eight eyes looking in all directions. Horseshoe crabs, only recently added to the class of arachnids based on molecular studies, are among the few that live in water, but come to mate on shore in dazzling nighttime rituals. 

Some arachnids, but comparatively few, can be deadly to humans; others, like ticks and mites, can be disease vectors. Most arachnids play vital roles in the ecosystem, however, such as regulating insect populations and eliminating pests from our farms and gardens; some mites help convert leaf litter to humus. Most are land predators, but some sea spiders live on the ocean floor. Arachnids are astonishingly diverse in habitat, size, and behavior. The vast majority we hardly notice. Those who get over the fear of spiders can enjoy their nimble legs, rapid runs, web-spinning expertise, and sometimes dazzling colors, particularly in the recently-discovered tiny peacock spiders of Australia, popularized in Jurgen Otto’s YouTube videos. Scientists are warming up to arachnids for their design inspirations.

See also “Don’t Be Frightened! It’s Just a Spider,” from Discovery Institute:

Dragline silk in spider webs is perhaps the best-known biomimetic target. It is highly desired as a material because of its strength and flexibility, so this article begins with spider silk news. Other arachnid design inspirations have recently been recognized.

Spider Networks

Among the properties that give spider silk its durability are beta-sheets of protein. A team from the University of Melbourne, publishing in Nature Communications, tackled the problem of making these sheets that spiders make look easy.

The high toughness of natural spider-silk is attributed to their unique β-sheet secondary structures. However, the preparation of mechanically strong β-sheet rich materials remains a significant challenge due to challenges involved in processing the polymers/proteins, and managing the assembly of the hydrophobic residues. Inspired by spider-silk, our approach effectively utilizes the superior mechanical toughness and stability afforded by localised β-sheet domains within an amorphous network. [Emphasis added.]

In the paper, the authors give high praise to the spider’s ability to make this “incredible” material.

The importance of how these secondary structures affect material properties is exemplified in naturally occurring dragline spider-silk; a natural polypeptide-based structure which displays a high tensile strength comparable to high tensile steel. Specifically, its excellent mechanical properties are attributed to the spatial arrangement of the amino acids within the polypeptide, which arrange to form higher-order β-sheet architectures through hydrogen bonding primarily from the hydrophobic amino acid residues (i.e. alanine). Surrounding these β-sheet architectures is an arrangement of semi-amorphous, highly extendable glycine-rich regions. This specific arrangement (i.e. composition and spatial) leads to spider silk displaying incredible toughness—a tensile strength between 0.88–1.5 GPa coupled with an extension at break of 21–27 %. This incredible mechanical potential garners significant interest towards the utilisation of polypeptides in synthetic materials, such as hydrogels, films and fibres for a wide range of applications, including tissue engineering and drug delivery.

Spider Medicine

Believe it or not, even spider venom provides inspiration. Another Australian team from the University of Queensland studied tarantulas, those denizens of nightmares, and found that “Spider venom [is] key to pain relief without side-effects.” That’s right; pain relief. Not only that, spider venom can stop pain without the risk of addiction that opioids cause. Dr. Christina Schroeder explains,

“Our study found that a mini-protein in tarantula venom from the Chinese bird spider, known as Huwentoxin-IV, binds to pain receptors in the body. “

“By using a three-pronged approach in our drug design that incorporates the mini-protein, its receptor and the surrounding membrane from the spider venom, we’ve altered this mini-protein resulting in greater potency and specificity for specific pain receptors.”

No side effects; no addiction; thank you, tarantulas!

Scorpion Cancer Therapy

Researchers at southern California’s City of Hope Cancer Center are finding ways to “repurpose” a scorpion toxin to benefit cutting-edge cancer treatment. See, “From scorpion to immunotherapy: City of Hope scientists repurpose nature’s toxin for first-of-its kind CAR T cell therapy to treat brain tumors.” Which scorpion is helping? The “death stalker” species, of all things! Watch the video to see how a small peptide in the venom helps CAR-T cell therapy achieve higher specificity in glioblastomas, saving brain cells during treatment. It has been the best agent so far, and clinical trials have begun — thanks to scorpions!

Scorpion Glow

Campers in the desert may know to bring ultraviolet lamps to look for scorpions. But why do their entire exteriors glow? Earlier studies suggested that the trait acts as a sunscreen or helps them find a mate at night. Two fluorescent molecules had been identified previously; Japanese scientists, publishing in the Journal of Natural Products, identified a third molecule that has the strongest fluorescent property. According to the American Chemical Society, the compound is “a phthalate ester previously shown to have antifungal and anti-parasitic properties in other organisms.” If so, fluorescence would represent a non-adaptive artifact. The fact that scorpions can manufacture three complex molecules and cover themselves with it, however, would suggest more is going on than scientists know about. The paper doesn’t mention any specific biomimetic applications, but one of the journal’s purposes is to investigate biological compounds with a view toward their potential usefulness.

Horseshoe Crab Lifesavers

The mysterious horseshoe crab, a living fossil that looks like an alien life form, is not a crab, but an arachnid. On early summer nights under a full moon at high tide, the animals emerge from the deep ocean and congregate by the hundreds of thousands on Delaware beaches to mate (NWF). Inside the body of this bizarre creature, says, is something that can save human lives.

Horseshoe crabs are remarkable animals, beautiful in their weirdness. These “living fossils” evolved 450 million years ago and have lived through at least five mass extinctions fatal to the majority of multicellular lifeforms on Earth. Sea-dwelling relatives of spiders, horseshoe crabs can lay millions of eggs, have four pairs of eyes, and (importantly to us) have blue blood containing amoeba-like immune cells. These horseshoe crab immune cells are analogous to the white blood cells of in our bodies, which protect us against a wide range of pathogens.

These amoeba-like cells, called amebocytes, contain a vital compound found only in horseshoe crabs.

Few people are aware that these cells from horseshoe crabs, called amebocytes, are indispensable for modern medicine. They are the only known source of Limulus Amebocyte Lysate (LAL), a reagent extraordinarily sensitive to the liposaccharide toxins produced by Gram-negative bacteria, which are responsible for 80% of cases of life-threatening sepsis in humans.

This creates a problem. Horseshoe crabs are an endangered species. Doctors can’t keep harvesting them in the wild, where some 30 percent die after their amebocytes are collected. Each year, some 600,000 animals have been collected during mating season in May and June. This cannot continue at that rate.

Now, however, scientists have found they can grow them in aquaculture. “These are welcome results for human patients at risk of life-threatening sepsis, and also for horseshoe crabs, since current harvesting practices are hardly sustainable,” the report says. With some 11 million people dying from sepsis each year, humans are learning to love their life-saving “weird” inhabitants of this amazing planet. “The horseshoe crabs continue to be lively and active in their new environment and even laid eggs.”

“Infectious disease is in our daily headlines and blood-borne bacterial infections leading to sepsis is the number one cause of untimely deaths worldwide. Humanity has now entered an era of pathogenic contagion that demands diagnostic and therapeutic breakthroughs of note. Our aquaculture method not only spares at-risk populations of horseshoe crabs: it also yields LAL that can finally be used in a quick, affordable, and ultra-sensitive assay for the early stages of sepsis, when time is of the essence for saving patients’ lives.”

So respect arachnids. Some of them are lifesavers, pain killers, and chemists extraordinaire. With only a few species examined so far, the potential for new discoveries among our eight-legged friends has barely begun.

Photo: Tachypleus gigas, a horseshoe crab, by Shubham Chatterjee / CC BY-SA.