Invertebrates

Arthropod Facts For Kids

Arthropods are amazing animals with jointed legs and hard outer shells! This group includes spiders, scorpions, centipedes, millipedes, crabs, lobsters, and shrimp (insects are arthropods too, but we covered them separately!). Arthropods are the most successful animals on Earth - over 80% of all known species are arthropods! They've been on Earth since ancient times. These creatures can survive in deserts, oceans, forests, caves, and even your house! Some have venom, others have pincers, and many have incredible superpowers! Want to learn more about these fascinating jointed animals?

Quick Facts About Arthropods

Type: Invertebrate (Arthropod)
Diet: Varies (carnivore, herbivore, or omnivore)
Size: 0.004 inches to 12 feet across
Weight: 0.00001 ounces to 44 pounds
Lifespan: Few months to 100+ years
Species: Over 1.2 million known species!
Where They Live: Worldwide (all habitats)
Baby Name: Varies by species
Group Name: Varies by species

What Do Arthropods Look Like?

All arthropods share key features! They have jointed legs (the name "arthropod" means "jointed foot"), hard outer shells called exoskeletons, and segmented bodies. But beyond that, they're incredibly diverse!

Arthropod sizes vary wildly! The smallest is a parasitic mite at 0.004 inches long - barely visible! The largest is the Japanese Spider Crab with legs spanning 12 feet - bigger than a car!

Arthropods have exoskeletons! Unlike animals with bones inside, arthropods wear their skeletons on the outside like armor. This protects them from predators and prevents water loss. As they grow, they must shed their old shell and grow a new, larger one - a process called molting!

Arachnids (spiders, scorpions, ticks, mites):

Eight legs attached to two body parts
No antennae or wings
Spiders have spinnerets for making silk
Scorpions have pincers and stinging tails
Many have multiple eyes (spiders can have 2-12!)

Myriapods (centipedes, millipedes):

Long bodies with many segments
Centipedes have one pair of legs per segment (15-177 pairs!)
Millipedes have two pairs of legs per segment (up to 750 legs!)
Centipedes are fast predators with venom
Millipedes are slow herbivores that curl when threatened

Crustaceans (crabs, lobsters, shrimp, barnacles):

Most live in water (a few on land)
Two pairs of antennae
Often have hard shells and claws
Many can regenerate lost legs!
Range from tiny water fleas to huge crabs

Many arthropods have amazing colors! Some spiders are bright blue or yellow. Certain millipedes glow in the dark! Crabs come in red, blue, purple, and orange. These colors can warn predators, attract mates, or help with camouflage!

Where Do Arthropods Live?

Arthropods live EVERYWHERE! They're found on every continent, in every habitat, from ocean depths to mountain peaks!

Spiders live almost everywhere! Every home has spiders hiding in corners, basements, or garages. Garden spiders build beautiful webs between plants. Tarantulas dig burrows in deserts. Diving bell spiders even live underwater in air-filled silk domes!

Scorpions love hot, dry places! Deserts are scorpion territory. They hide under rocks during scorching days, then hunt at night. Scorpions glow bright blue-green under ultraviolet light - scientists aren't sure why! Some scorpions can survive being frozen solid!

Centipedes prefer dark, damp spots! They live under logs, rocks, and leaf litter. House centipedes lurk in basements and bathrooms. Despite having many legs, centipedes are fast runners! They hunt other arthropods and small creatures at night.

Millipedes live in soil and leaf litter! They're decomposers, eating rotting plant matter. Millipedes burrow through soil, helping break down dead leaves. When threatened, many curl into tight spirals. Some spray defensive chemicals that smell terrible!

Marine arthropods dominate the oceans! Crabs scuttle along ocean floors. Lobsters hide in rocky crevices. Shrimp swim in huge schools. Barnacles cement themselves to rocks, ships, and even whales! Horseshoe crabs (actually more related to spiders!) crawl on seafloors.

Some arthropods are parasites! Ticks attach to animals and drink blood. Lice live in hair and feathers. Some mites burrow into skin. Parasitic arthropods can spread diseases, making them dangerous despite their tiny size.

Many arthropods make homes! Spiders build intricate webs. Trapdoor spiders create burrows with hinged silk doors. Social spiders work together to build massive communal webs that can span entire trees!

What Do Arthropods Eat?

Arthropods have incredibly diverse diets!

Predatory arthropods (hunters):

Spiders catch insects in webs or actively hunt them
Jumping spiders stalk prey like tiny cats
Scorpions grab prey with pincers, then sting it
Centipedes inject venom to paralyze prey
Praying mantis wait motionless, then snatch insects
Crabs are scavengers and predators, eating almost anything

Herbivorous arthropods (plant eaters):

Millipedes eat decaying leaves and plant matter
Some mites eat plants and fungi
Certain crabs graze on algae
Wood lice (pill bugs) eat rotting wood

Filter feeders:

Barnacles filter tiny organisms from water
Some shrimp filter plankton
Krill (tiny shrimp-like animals) are crucial food for whales!

Blood feeders:

Ticks attach to animals and drink blood for days
Some mites feed on blood
These can spread serious diseases

Spiders have unique eating habits! They can't chew food. Instead, they inject digestive juices into prey, liquifying the insides. Then they suck out the liquid meal! The empty insect shell is all that remains.

Many arthropods are decomposers! Millipedes, pill bugs, and certain mites break down dead plants. They're nature's recyclers, returning nutrients to soil. Without them, dead leaves would pile up everywhere!

Crustaceans are ocean's cleanup crew! Crabs, lobsters, and shrimp eat dead fish and animals. They're scavengers that keep oceans clean. Hermit crabs are especially fun - they live in abandoned snail shells and switch to bigger shells as they grow!

Some arthropods eat surprising things! Clothes moths eat wool and fur. Booklice eat mold growing on books. Carpet beetles eat dead skin, hair, and fabric. Many "pest" arthropods eat human food like flour, grains, and stored products.

Baby Arthropods

Arthropods reproduce in fascinating ways!

Most arthropods lay eggs! Females lay eggs in protected spots - under bark, in soil, in water, or in silk egg sacs. Some species lay dozens, others thousands! Eggs hatch into young that look different from adults.

Many arthropods go through metamorphosis! Baby crustaceans often look nothing like adults. They go through several stages, changing shape each time they molt. Horseshoe crabs molt 16-17 times before reaching adult size!

Spiders hatch from egg sacs! Mother spiders wrap hundreds of eggs in silk. When spiderlings hatch, they often stay together briefly. Then they "balloon" - shooting silk into air and floating away on wind! This is how spiders travel long distances.

Scorpions give live birth! Unlike most arthropods, scorpions don't lay eggs. Babies are born alive! Mother scorpions carry all their babies on their backs for 1-2 weeks. She protects them fiercely until they're ready to hunt alone.

Centipedes and millipedes hatch with few legs! Baby centipedes might have only 4 pairs of legs. With each molt, they add more segments and legs. Full-grown millipedes can have 200+ legs (despite the name meaning "thousand feet"!)

Crabs go through larval stages! Baby crabs look like tiny aliens - nothing like adult crabs! They drift in ocean currents, molting several times. After several weeks, they settle to the bottom and transform into recognizable baby crabs.

Some arthropods care for young! Wolf spiders carry egg sacs attached to their spinnerets. When spiderlings hatch, they climb on mom's back and ride around for days! Certain scorpions protect young for months. Most arthropods, though, provide no parental care.

Growth requires molting! Because their skeletons are on the outside, arthropods must shed them to grow. Before molting, a new soft shell forms under the old one. The old shell splits, and the arthropod crawls out. The new shell is soft for hours or days, then hardens. During this vulnerable time, many hide!

Why Are Arthropods Special?

Arthropods are designed with incredible adaptations! Their hard exoskeletons, jointed legs, and diverse body plans have made them the most successful animals ever. They've colonized every habitat and survived mass extinctions that wiped out dinosaurs!

Arthropods are crucial for ecosystems! Spiders control insect populations. Crabs and shrimp clean oceans. Millipedes recycle dead plants. Without arthropods, ecosystems would collapse! They're vital parts of food chains, feeding countless animals.

Arthropods help humans! Horseshoe crab blood saves lives by testing medical equipment. Crabs, lobsters, and shrimp provide food for millions. Spiders eat mosquitoes and flies. Scientists study arthropods to develop new materials and technologies inspired by nature!

Some arthropods are dangerous! Venomous spiders and scorpions can harm humans. Ticks spread Lyme disease and other illnesses. Some centipedes have painful bites. However, most arthropods are harmless and beneficial!

Many arthropod species face threats! Pollution and habitat loss affect arthropods. Some species have gone extinct. Protecting arthropods means protecting entire ecosystems since they're so interconnected with other life!

Everyone can help arthropods! Reduce pesticide use - it kills helpful arthropods too. Leave some wild areas in yards for arthropod habitats. Learn to identify helpful vs. harmful species. Respect ocean life when visiting beaches. Small actions protect these amazing animals!

Cool Facts About Arthropods!

Spiders produce silk stronger than steel! Spider silk is one of the strongest materials in nature. A strand as thick as a pencil could stop a jetliner! Different spiders make different types of silk - some for webs, others for wrapping prey, and some for making parachutes to fly on wind!
Scorpions glow under ultraviolet light! All scorpions fluoresce bright blue-green under UV light. Scientists still don't know exactly why! This makes finding scorpions at night easy - just use a blacklight. Scorpions have been on Earth since ancient times!
Horseshoe crabs have blue blood! Their blood contains copper instead of iron, making it blue. This blood is incredibly valuable - it's used to test medicines for contamination. One quart of horseshoe crab blood is worth $15,000! Horseshoe crabs are ancient creatures that have changed very little over time!
Coconut crabs are giant robbers! These enormous crabs can grow 3 feet across and weigh 9 pounds. They're strong enough to crack coconuts with their claws! Coconut crabs can climb trees and have been known to steal shiny objects from campsites!
Tarantulas can regrow lost legs! If a tarantula loses a leg to a predator or accident, it can regrow it during the next molt. Young tarantulas might regrow a perfect replacement. Older ones might regrow a smaller version. They can live 25+ years!
Some spiders hunt fish! The fishing spider walks on water and can dive to catch small fish! They feel vibrations on the water surface to detect prey. When a fish swims by, the spider dives underwater and grabs it!
Centipedes have venom claws! Their first pair of legs are modified into venomous fangs called forcipules. Giant centipedes can grow 12 inches long and catch mice, lizards, and birds! Their venom is painful to humans but rarely dangerous.
Mantis shrimp have the fastest punch! These marine crustaceans strike so fast they create bubbles that collapse with a flash of light! The punch reaches 50 mph and can break aquarium glass. They have the most complex eyes in nature - seeing colors we can't imagine!
Ticks can survive extreme conditions! Ticks can live 3+ years without food! They survive freezing, drought, and being underwater. Some tick species can detect carbon dioxide from animals 100 feet away, helping them find hosts.
Japanese Spider Crabs are giants! With legs spanning 12 feet, they're the largest arthropods on Earth. They can live 100 years! Despite their size, they're gentle and eat dead animals on the ocean floor. They look like something from a monster movie!