10 Giant Invertebrates You Don’t Want to Meet

In this creepy account of spineless giant animals, we will tour the planet and discover record holding monster invertebrates, including the kings and queens of major categories of molluscs, crustaceans, spiders, and centipedes – including 3-foot hermit crabs, dinner plate-sized spiders, and a crayfish bigger than a small dog. When the largest animals without backbones are considered, it is clear that when encountering those of unimagined sizes it is best to simply stay out of the way…

10. Japanese Spider Crab

The largest known arthropod on the planet, the Japanese Spider Crab Macrocheira kaempferi dwarfs other crustaceans, possessing a science fiction worthy 12-foot maximum legspan and weighing up to 44 pounds. The animals dwell at depths from 160 feet to 2,000 feet and use their elongated claw-bearing arms to gather prey. The sharp, powerful claws could injure a human and are to be avoided. Feeding on a combination of plants and animals, some Japanese Spider Crab may feed on the dead bodies of a variety of animals on a frequent basis, while other individuals can be found that concentrate on prying open live shellfish and eating the contents. While the carapace is massive, it is dwarfed by the disproportionately long spindly legs of this species.

The Japanese Spider Crab does not only go out on the hunt for prey, it also goes to incredible lengths to disguise itself, earning the title of “decorator crab” in the process. Seashells, seaweed, sponges, and anemones may actually be cemented by the crabs to their carapace, disguising the enormous crab to the point where it resembles a submerged, sealife colonized rock. Ironically, the largest spanning crustaceans on Earth start life as nearly microscopic larvae that are planktonic in form, drifting through the ocean before gaining mass and starting on their path to becoming monsters.

9. Tasmanian Giant Freshwater Lobster

Black, sleek, and armed with massive claws, the Tasmanian Giant Freshwater Lobster Astacopsis gouldi is a gigantic crayfish that no one would want to handle without extreme caution. Looking like a model designed to scare a gullible audience, the all-too-real monster crustacean is a massive and dreadful looking creature that can reach lengths of 2.5 feet and a weight of over 11 pounds. The largest crayfish in the world, this Tasmanian endemic also firmly holds the title of largest freshwater invertebrate on Earth but ironically inhabits small watercourses.

Despite the physical injuries that could result from a careless encounter with this enormous dark crayfish, the stream dwelling species faces a greater degree of danger from humans than it could ever pose. Overfishing has resulted in depletion of large breeding adults, which has combined with habitat destruction from logging impacts to cause the animals to become listed as endangered. Dependant on cool, clean water, just 100,000 individual freshwater lobsters remain in the wild, leading to vigorous conservation efforts aimed at curtailing overfishing and limiting logging in sensitive areas to avoid runoff, siltation and warming due to loss of stabilizing vegetation and shade. Able to live for 30 years, the giant lobsters now benefit from a ban on fishing since 1998 but depend on habitat protection for continued survival.

8. Giant Huntsman Spider

Discovered by German arachnologist Peter Jäger on an expedition to Laos in 2001, the Giant Huntsman Spider Heteropoda maxima is a little known, enormous arachnid with a legspan of up to 1-foot in breadth. Such an enormous legspan makes it the largest spider on the planet, by physical size. The Giant Huntsman spider has a visually shocking hairy tiger striped pattern, with bold alternations of black and beige to rusty sections along its legs and on the abdomen and cephalothorax. Feeding on a wide variety of prey including cockroaches, the high energy and aggressively tempered Giant Huntsman is so named for chasing down its prey instead of building a web and lying in wait like a stereotypical spider.

With what have been described as crab-like legs, the Giant Huntsman can run rapidly from side to side as well as forward, combining incredible agility with eerie looking and highly prominent fangs to capture and subdue its prey before injury to the spider can occur. Agility enhancing adaptations include twisted joints and an outwardly spread stance. Interestingly, male Giant Huntsman Spiders have longer legs than females, but the sex with the larger body size is the female. The somewhat startling discovery of the Giant Huntsman Spider highlights the fact that new giant invertebrates may be waiting to be discovered and new finds are not limited to small or harmless invertebrates.

7. Amazonian Centipede

Centipedes are scary and sometimes highly dangerous to humans due to their powerful venom and agility. They can reach unbelievable sizes, and have the predatory potential that might make even a seasoned arthropod biologist shudder. The grand ruler of centipedes is the enormous Amazonian Giant Centipede Scolopendra gigantean, a master predator that can take down birds, mice, spiders, and roosting bats. And by the way, it can grow to a foot long. Due to its size and appearance, this nightmarishly scaled up centipede looks like a terrible machine from a science fiction film come to life.

Hailing not only from the Amazon but also inhabiting parts of the Caribbean, the Amazonian Giant Centipede is perhaps at its most impressive as an accomplished but creepy hunter of bats in caves, where it clambers up walls and hangs from cave ceilings with its strong multitude of legs and then strikes out at passing bats, incapacitating them with its powerful venom. Like smaller centipedes, this giant is equipped with massive, venom releasing fangs that are actually modified front legs called forcipules. The wicked hooks can easily pierce human skin if the centipede is alarmed, injecting a soup of chemicals including cardiac depressors and complex amino acids that will bring death to birds, mammals, and even snakes that fall prey to the giant centipede. In addition to venom, the centipede uses force, wrapping its legs around victims to quell their struggle and secure a meal. Humans, if bitten by this arthropod, may suffer chills, agonizing pain, and swelling.

6. Giant African Millipede

Millipedes may be thought of as minute, but the aptly named Giant African Millipede Archispirostreptus gigas ranks first in size among these supposedly thousand-footed animals. Native to the sub-tropical rainforests of Western Africa, a specimen of the king or queen of millipedes may reach a foot in length. Favoring warm, moist places, Giant African Millipedes are known as detritivores, which are herbivores adapted to feed on dead and decaying plant material over live plants. Massive plates cover the millipede’s body, which is supple and can be formed into a curled, circular shape, making it much more awkward for a predator to gather up and prey upon the millipede. If that is not enough, the Giant African Millipede may draw on chemical warfare to ward off predatory attempts.

Not to be confused with the venomous centipedes that actually inject venom in the course of hunting, millipedes want to mind their own business but are poisonous, rather than venomous as they do not inject toxins by biting, having weak jaws, but instead release or contain chemicals that are harmful to contact or ingest. In the case of the African Giant Millipede, disgusting and potentially irritating hydrogen cyanide gas can be released if the millipede is disturbed by a predator or even a curious human.  The Giant African Millipede is a nocturnal animal, avoiding exposure to daytime predators as it patrols the forest floor for decaying food under the cover of darkness. Millipedes are extremely unusual animals in a variety of respects, yet another of quirk being their strange mode of respiration. To breath, millipedes collect air through holes in their body known as spiracle. Thus, millipedes are placed at risk of drowning if excessively soaked.

5. Colossal Squid

It is not the giant squid of popular imagination that is the most massive on the planet. It gets better, or for those with a phobia of squid, worse. The Colossal Squid Mesonychoteuthis hamiltoni, made known through examination of specimens collected in Antarctic waters, is the largest invertebrate on the planet. The potential length of this species is estimated at 46 feet. The eyes alone, the largest eyes of any life form on the planet, may exceed 12 inches in diameter, while movable hooked claws and a massive beak allow this giant to inflict injuries visible on the skin of sperm whales that are understood to prey upon the squid, but not without retribution from the enormous molluscs.

Colossal Squid have attracted significant interest from researchers through the discovery of remains and occasional live specimen collections. Notable is the ability of this species to weigh in at over 1100 pounds, with females reaching a greater potential size than males. An ambush predator that reaches its enormous size through a biological phenomenon called abyssal gigantism, the Colossal Squid is equipped not only with a razor sharp, massive cutting beak but has sharp, flesh-tearing hooks that include those that can swivel, inflicting damage on predators or prey at strategic angles.

4. Australian Trumpet

Known mostly as 1 to 2-inch garden pests or on occasion, as a French delicacy, snails are considered small by most people. We aim to change that perception by bringing the world’s largest snail to popular attention. An ocean-going monster, the world’s largest living snail represents biological reality far beyond anyone’s typical imagination. Native to Northern Australian waters and the coasts of nearby regions including Papua New Guinea, the Australian Trumpet Syrinx aruanus is a gigantic species of predatory whelk little known to ecologists but famous in the shell collecting community. This species may have a shell length of no less than 3 feet, with a potential weight of up to 40 pounds.

Specially adapted to feed on huge marine worms, the Trumpet Snail is an adept but still mysterious predator that clearly deserves more scientific investigative attention. With their ecology little known, further investigation into their life history and conservation status would be wise. As a direct development species, eggs from egg cases deposited by females hatch into fully formed miniature snails which spread out into their habitat from the site in contrast to species that are distributed as plankton and thus better able to recolonize depleted sites. Occurring from the intertidal shallows down to depths of 164 feet, the snails have a round mid section combined with a narrow rear, giving a trumpet-like appearance.

3. Coconut Crab

While the title for largest crab goes to the Japanese Spider Crab, a highly aberrant species of land-dwelling hermit crab holds the record for largest land-dwelling arthropod. Described as monstrous by Charles Darwin, the Coconut Crab Birgus latro is the only arboreal hermit crab family member on the planet, setting another crustacean record through its conquest of trees as it climbs to escape any threats. Reaching up to 3 feet in length, the huge creatures patrol islands in the Indian Ocean and South Pacific Ocean not only for fallen coconuts, broken open with their enormous, potentially dangerous claws, but may also feed on other crab species and food left out by humans. Coconuts are not only eaten by coconut crabs but are also used as burrow building material.

Coconut Crabs retire to burrows lined with coconut fiber, taken from the hairy husks of the coconut. Unlike typical hermit crabs, the Coconut Crab does not wear a discarded gastropod shell except as a small juvenile, but develops a hard and damage resistant exoskeleton with age. If the Coconut Crab falls while climbing, it can land without damage and walk away from the impact site. Classed as data deficient by the International Union for Conservation of Nature, the Coconut Crab has sadly been extirpated in areas of intense human settlement including Australia and Madagascar. While additional threats have come from introduced predators such as rats, Coconut Crabs have been known to capture and eat rats on occasion. Despite their huge size and terrestrial lifestyle, the young start out as barely visible planktonic larvae that arrive on land once sufficiently developed.

2. Giant Forest Scorpion

Scorpions of any size may inspire fear in humans, but the largest of scorpions have to be seen to be believed and could lead to a massive demand for steel-toed boots among jungle explorers. Measuring up to 9-inches-long, the Giant Forest Scorpion Heterometrus swammerdami of India and Sri Lanka is the most massive scorpion species on the planet. Weighing up to 2 ounces, the massive creatures possess less venom than many other scorpions, relying more on their crushing power contained within lobster-like claws to dispatch prey.

Black in color, the gigantic scorpion has a disproportionately massive pair of claws that dwarf the midsection of the body, while the venom-bearing stinger is set on a tail of equally disproportionate thickness. The venom may not be as concentrated as that of smaller and weaker scorpions due to the beastly arthropod’s ability to rely on its brute strength to defend itself and bring down prey in a variety of circumstances. However, the animals have a copious amount of venom thanks to their sheer size that will be injected without very much hesitation if provoked. With their magnificent appearance, these largest of scorpions are sought after by arthropod hobbyists as exotic specimens or pets, to be kept with ample caution.

1. Giant Isopod

Many of us have not heard of an isopod but the largest species, the Giant Isopod Bathynomus giganteus, is not a creature you will easily forget (because it’ll haunt your nightmares). A relative of familiar garden variety pillbugs, the Giant Isopod is an exceedingly creepy looking crustacean with prehistoric-looking armor plating to protect it from predators. An accomplished scavenger, feeding on items ranging from dead fish to sunken whale carcasses, Giant Isopods are able to scavenge or tear apart a wide variety of prey items with its powerful jaws that act like a multi-tool to process food. As they may even attack trapped fish being brought up by trawlers, isopods can be classed as true opportunists as well as scavengers.

There can be little doubt that Giant Isopods might also go after human remains, given the chance, and one would not want to put one’s fingers in the way of the creature’s powerful, carcass disposal ready jaws. Distributed widely across the world’s oceans, Giant Isopods may reach just over 14 inches in length, owing their enormous size to deep sea gigantism. The aberrant crustaceans are primarily solitary creatures, living at depths ranging from 550 to 7,020 feet, with bizarre exoskeleton shielded eyes that are fixed in place and look uncannily machine-like. Yet more eerily, the eyes contain a reflective layer in the back called a tapetum that makes the eyes glow when viewed. While a useful adaptation, the trait seals the Giant Isopod’s identity as a real-life B movie sea monster.

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