Six legged animals, also known as hexapods, are a unique and fascinating group of creatures. From ants marching in lines to beetles scurrying under logs, six legged critters are everywhere if you know where to look.
If you’re short on time, here’s a quick answer to your question: Insects, spiders, centipedes, and millipedes are the main types of 6 legged animals. They can be found worldwide in virtually every habitat and play vital ecological roles.
In this comprehensive guide, we will explore the key types of hexapods, their anatomy and physiology, evolutionary origins, ecological roles, and some of the most unique species from around the world.
The Main Types of 6 Legged Animals
Insects
Insects are the most diverse and abundant group of animals on Earth, with over 1 million described species. They have three main body parts – head, thorax and abdomen – along with six jointed legs, compound eyes, and two antennae.
Some common insect orders include Coleoptera (beetles), Lepidoptera (butterflies and moths), Hymenoptera (ants, bees, wasps) and Diptera (flies). Insects play vital ecological roles as pollinators, decomposers, predators, and prey. Some are beneficial while others are pests or carriers of disease.
Spiders
Spiders belong to the arthropod group Chelicerata and have eight legs, simple eyes, fangs, and no antennae. There are over 45,000 known spider species inhabiting every continent except Antarctica. Spiders are carnivorous and use silk webbing and venom to subdue their prey.
Some build intricate webs to trap insects while others hunt actively. Spider bites are typically harmless to humans, but some species like black widows and brown recluses can be medically significant. Spiders help control insect populations and are an important part of many ecosystems.
Centipedes
Centipedes are predatory arthropods belonging to the class Chilopoda. There are over 3,000 centipede species found worldwide, except in polar regions. They have long, flattened bodies with one pair of legs per body segment, typically 15 to 177 pairs in total.
Despite the name “centipede”, no known species has exactly 100 legs. Centipedes are venomous and use pincer-like claws to capture prey like insects, spiders, and small reptiles. House centipedes are common in buildings and help control household pests.
Large tropical species can exceed 12 inches in length.
Millipedes
Millipedes are arthropods in the class Diplopoda, characterized by having two pairs of legs on most body segments. There are over 10,000 millipede species found globally, except Antarctica. They have more legs than centipedes, ranging from 36 up to 750.
However, no known millipede has exactly 1,000 legs. Millipedes are generally slow-moving detritivores, feeding on decaying plant matter and fungi. They help recycle nutrients back into the soil. Millipedes can secrete toxic liquid or hydrogen cyanide for defense but are not harmful to humans.
The giant African millipede can reach over 12 inches long.
Anatomy and Physiology
Exoskeletons
Most six legged animals like insects and arthropods have a tough outer exoskeleton covering their body. This exoskeleton protects their internal organs and tissues from the external environment. Made up of a compound called chitin, the exoskeleton provides structural support as well as sites for muscle attachment so the animals can move.
Molting or shedding the exoskeleton is necessary for growth in these animals. According to Britannica, molting happens several times as the animals progress from juvenile stages to adulthood.
Segmented Bodies
Insects and other six legged creatures have segmented bodies, which means their bodies are divided into sections. These well-defined divisions with independent nerve supply allows for greater mobility and adaptations.
According to veterinary experts at Washington State University, the three main body segments of insects are the head, thorax and abdomen. The head houses sensory organs like eyes and antennae as well as mouthparts.
The thorax bears the legs and wings while the abdomen contains organs related to digestion, reproduction and respiration.
Specialized Appendages and Mouthparts
The six jointed legs attached to the thorax provide stability and mobility. Apart from legs, six legged animals could also have other specialized appendages like:
In terms of feeding, insects and arthropods have mouthparts specialized for biting and chewing or piercing and sucking. According to DKfindout, butterflies and moths have a tubular proboscis to drink nectar while mosquitoes have a piercing stylet to penetrate skin and draw blood.
Category | Examples | Mouthpart Type |
---|---|---|
Herbivorous insects | Grasshoppers, Caterpillars | Chewing |
Parasitic insects | Mosquitoes, Fleas | Piercing-sucking |
As we can see, six legged creatures have evolved specialized body parts and physiology to thrive in their unique environmental niches.
Evolutionary Origins
The Arthropod Lineage
Arthropods are characterized by their segmented bodies and jointed appendages. The earliest arthropods emerged during the Cambrian explosion over 540 million years ago. The first arthropods likely evolved from worm-like ancestors and developed hardened exoskeletons for protection.
Over time, arthropods diversified into the major groups we know today including insects, arachnids, crustaceans and myriapods.
The oldest known six-legged fossil is Pneumodesmus newmani, a millipede-like creature that lived 428 million years ago during the Silurian period. This primitive hexapod displayed evidence of spiracles and tracheal systems – adaptations that allowed arthropods to breathe air and move onto land from the sea.
Adaptations Over Time
The success of six-legged arthropods is largely thanks to evolutionary adaptations over millions of years:
- Exoskeletons – For structure, protection, points of muscle attachment.
- Segmented bodies – Allows flexibility and specialized body parts/appendages.
- Tracheal respiration – Efficient oxygen delivery for active land life.
- Compound eyes – Detailed vision including detection of motion.
Further adaptations enabled radiation into diverse ecological niches. Insects evolved wings for dispersal and legs adapted for running, jumping, swimming, digging, grasping prey, or collecting pollen. Advanced sensory systems, defensive chemicals, cryptic coloration and complex behaviors also developed.
Today there are over 1 million described species of hexapods including insects, springtails, centipedes and millipedes. They represent over 80% of all known living animal species – a testament to the success of their body plan.
Ecological Roles
Herbivores
Six-legged herbivores play a crucial role in their ecosystems by consuming plant matter. Some common examples include grasshoppers, caterpillars, ants, and termites. As primary consumers, they provide food sources for predators higher up the food chain while also dispersing seeds and pollen.
Their feeding habits help shape the diversity and distribution of plant communities.
Caterpillars, for instance, can defoliate entire trees and bushes by devouring leaves. This pressures plants to evolve chemical defenses while providing a feast for insectivorous birds when caterpillars are abundant.
Meanwhile, ants protect certain plants from being overgrazed by other insects, in exchange for nectar or nutrients. By transporting and burying seeds, ants also aid in seed dispersal and germination for numerous plant species.
Predators
Six-legged predators such as dragonflies, centipedes, spiders, and praying mantises help control prey populations like mosquitos, flies, beetles, and other small invertebrates. They are an integral part of natural biocontrol systems that maintain balance within food webs.
Their hunting and stalking techniques have also evolved remarkably effective mechanisms for capturing elusive prey.
For example, trap-jaw ants have spring-loaded mandibles that snap shut faster than any other animal appendage on Earth, enabling them to seize small insects in the blink of an eye. Meanwhile, orb-weaving spiders construct intricate webs that passivey entrap unsuspecting insects.
Such specialized adaptations showcase the diversity of predatory strategies among six-legged hunters.
Detritivores
Detritivores feed on decaying organic matter, recycling dead plant and animal material back into the ecosystem as nutrients. On land, insects like burying beetles, termites, and millipedes fill this niche.
Their digestive systems harbor symbiotic bacteria and fungi that help decompose complex substances like cellulose and lignin.
For example, termites alone are estimated to consume 11-22% of the world’s dead plant biomass. Their efficient biodegradation of wood and leaf litter releases key compounds like nitrogen, phosphorus, and potassium that enrich tropical soils.
By consuming waste material and excreting nutrient-rich feces, detritivorous insects thus facilitate natural recycling pathways.
Pollinators
Many insects with six legs serve as essential pollinators for flowering plants. Bees, butterflies, moths, beetles, and flies transport pollen from one blossom to another as they collect nectar and other floral rewards.
This fertilization service is crucial for producing seeds, fruits, and genetic diversity in plant populations.
According to the UN Food and Agriculture Organization, nearly 75% of the world’s crops benefit from animal pollination, with bees pollinating 70% of major crops. Declining insect pollinator numbers threaten global food security and ecosystem health.
Conserving their habitats and avoiding overuse of pesticides are key steps toward protecting pollination services.
Unique Species
Giant Centipedes
Giant centipedes are predatory arthropods that can reach sizes of up to 12 inches in length. These venomous creatures have elongated, segmented bodies with 15 to 177 pairs of legs. They are found primarily in tropical and subtropical regions around the world.
Some of the most notable giant centipede species include Scolopendra gigantea, also known as the Amazonian giant centipede, which can exceed a foot in length. Another is Scolopendra cataracta, the Vietnamese centipede, which holds the record for having 177 pairs of legs.
Giant centipedes are fierce nocturnal hunters that typically feast on snakes, frogs, mice, lizards, and even bats. They subdue their prey using their sharp fangs and venomous claws. Despite their intimidating appearance, centipede bites are rarely fatal to humans.
Trapdoor Spiders
Trapdoor spiders comprise over 30 different spider species that construct underground burrows with a hinged trapdoor made of soil, vegetation, and silk. These cryptic spiders lie in wait for passing prey to ambush.
Some of the most notable trapdoor spider species include the Gondwanan trapdoor, which is distinguished by its reddish hue and large size reaching over 2 inches in body length. The African trapdoor spider also grows quite large and possesses a lengthy lifespan of over 20 years.
Trapdoor spiders snatch their prey by bursting out from their burrows and pulling victims inside with their strong front legs. They typically feast on insects but will occasionally catch small reptiles and mammals. Their venom can be quite painful to humans but is not lethal in most cases.
Bombardier Beetles
Bombardier beetles are ground beetles that eject hot noxious chemical spray in order to deter would-be predators. They derive their name from how they bombard attackers with pulses of their scalding defensive secretion.
There are over 500 species of bombardier beetles. When threatened, they mix hydroquinones and hydrogen peroxide inside their abdomen to produce temperatures reaching the boiling point. A structure called the pygidial gland stores and aims this boiling spray.
A few squirts of their hot defensive spray is enough to irritate skin and damage small insect assailants. Bombardier beetles can emit their boiling secretion a dozen times without needing to produce more, making them a formidable foe.
Orchid Mantises
The orchid mantis comprises over 30 carnivorous species that exhibit spectacular camouflage resembling flower petals. Most are native to Southeast Asia and South Africa.
Some of the most stunning species include Hymenopus coronatus, also known as the orchid mantis, which mimics parts of the orchid flower. The pink orchid mantis is also quite spectacular with its bright pink hue that provides remarkable camouflage among flowers.
Orchid mantises are ambush predators that wait motionless for prey to come within striking range. Their raptorial front legs can unleash an exceptionally speedy strike to grab victims. They mostly eat other insects as well as the occasional small reptile or amphibian.
Conclusion
With over a million described species, hexapods are one of the most successful branches on the tree of life. From tiny springtails to massive Hercules beetles, six legged creatures come in every shape and size imaginable.
While we often overlook these small invertebrates, they play integral roles in ecosystems worldwide. Learning about their diversity helps us appreciate the interconnectedness of all living things on our planet.