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Invertebrates · 13 species guides

Arachnids: Spiders, Scorpions & Harvestmen

Arachnids are eight-legged arthropods that include spiders, scorpions, harvestmen (daddy longlegs), ticks and mites; they lack antennae and wings, and most are predators that use fangs or claws rather than chewing mandibles like insects do.

Eight legs
Adult arachnids have eight legs. Insects have six.
No antennae
Arachnids lack antennae; insects have a pair.
Spider body plan
Spiders have two body regions (cephalothorax and abdomen) and fangs; insects have three regions.
Scorpion metasoma
Scorpions carry a segmented tail with a venomous stinger; spiders do not.

Arachnids are not insects. Eight legs, two main body regions in spiders, and no antennae are the starting rules. Daddy longlegs myths — most venomous spider, or not a spider at all — need careful sorting: harvestmen are arachnids but not spiders; cellar spiders are true spiders. Medically important widows and recluses are a tiny minority of species.

Most spiders are harmless to people and suppress insect pests for free. Scorpions sting with a tail spine; spiders bite with fangs. Habitat specialists and island endemics can be threatened even when common garden spiders remain abundant. This page holds the eight-leg separation and the confusion pairs; linked guides cover the species people actually search for. WARN arachnid guides linked here cover spiders, tarantulas, widows, recluses, jumping spiders, daddy longlegs and scorpions. Household encounters almost always involve harmless hunters; medically significant species are geographically limited and rare relative to total spider diversity.

Key facts

  • Arachnids have eight legs and are not insects.
  • Spiders, scorpions and harvestmen are all arachnids.
  • Most spiders are harmless to people; a few genera are medically important.
  • Daddy longlegs can mean harvestmen or cellar spiders — different animals.
  • Scorpions sting with a tail spine; spiders bite with fangs.
  • Habitat loss and persecution remove predators that control insect pests.

How to recognise them

The features that separate this group in the field, in the order they are usually most useful.

Eight legs
Adult arachnids have eight legs. Insects have six.
No antennae
Arachnids lack antennae; insects have a pair.
Spider body plan
Spiders have two body regions (cephalothorax and abdomen) and fangs; insects have three regions.
Scorpion metasoma
Scorpions carry a segmented tail with a venomous stinger; spiders do not.
The confusion pairs
Harvestman versus cellar spider: harvestmen have a single oval body; spiders have a narrow waist. Black widow versus false widow: hourglass marks and medical risk differ by species and region.

13 arachnids guides

Search or filter by conservation status. Every guide carries sourced facts, IUCN status and FAQs.

Showing 1-13 of 13 animals

Animal group
Glossy black widow spider hanging in its web showing the red hourglass marking
Least Concern

Invertebrates

B

Black Widow Spider

Latrodectus mactans

The glossy black spider with the red hourglass

North America

Open guide
Brown recluse spider showing violin marking on cephalothorax
Not Evaluated

Invertebrates

B

Brown Recluse Spider

Loxosceles reclusa

The violin-marked spider of the American South

North America

Open guide
Solifugid camel spider with large chelicerae and hairy legs on desert sand, body length modest relative to leg span
Not Evaluated

Invertebrates

C

Camel Spider

Order Solifugae — over 1,000 described species; not spiders and not camels

Neither camel nor spider — and almost everything the internet says about it is wrong.

Deserts and arid regions worldwide · South-western United States, Middle East, North Africa and Central Asia

Open guide
Harvestman daddy longlegs with a tiny oval body and extremely long thin legs on damp forest bark
Not Evaluated as a group

Invertebrates

D

Daddy Longlegs

Name shared by Pholcidae (cellar spiders), Opiliones (harvestmen) and sometimes Tipulidae (crane flies)

Three different animals share the name — and none of them is the world's most venomous spider.

Worldwide in temperate and tropical regions · Cellars, sheds and vegetation in Britain and Europe

Open guide
Giant house spider with long brown legs resting on a pale surface showing its large size
Least Concern

Invertebrates

G

Giant House Spider

Eratigena atrica

Britain's large but harmless funnel-weaving house spider

Europe

Open guide
Large flat-bodied huntsman spider with long legs spread wide on a pale indoor wall
Not Evaluated

Invertebrates

H

Huntsman Spider

Family Sparassidae — e.g. Heteropoda venatoria (Linnaeus, 1767) and related genera; over 1,300 described species

The spider in most viral photographs — large, fast, flat, and near-harmless to people.

Tropical and subtropical regions worldwide · Australia, Asia, the Americas and Mediterranean Europe

Open guide
Close-up of a fuzzy jumping spider with large round front eyes on a leaf
Least Concern

Invertebrates

J

Jumping Spider

Salticidae

The big-eyed spider that pounces on its prey

Africa · Asia

Open guide
European garden spider in the centre of a dew-spangled circular orb web between hedgerow branches
Family page

Invertebrates

O

Orb-Weaver

Family Araneidae — over 3,000 described species worldwide

The spider that builds the classic wagon-wheel web — and rebuilds it every day.

Worldwide except polar extremes · Gardens and woodland across Britain and Europe

Open guide
Male peacock spider with iridescent abdominal fan raised and third legs extended in a courtship display on leaf litter
Not Evaluated

Invertebrates

P

Peacock Spider

Genus Maratus — family Salticidae (jumping spiders); roughly 100 described species, mostly Australian

Five millimetres of iridescent fan and leg-waving — the spider that went viral and still lacks a proper field guide.

Australia · New Guinea and nearby islands

Open guide
Desert scorpion with arched tail on warm sand
Order page

Invertebrates

S

Scorpion

Order Scorpiones — roughly 2,500 described species in about 22 families

440 million years old, glows under UV, and only about 25 species can seriously harm a person.

Every continent except Antarctica · Deserts, grassland, forest, caves and mountains

Open guide
Orb-weaver spider centred in a dew-laden circular web between meadow grasses at dawn
Order page

Invertebrates

S

Spider

Order Araneae — over 50,000 described species in more than 120 families

Silk, venom and patience — the most successful land predators you mostly notice by accident.

Every continent except Antarctica · From deep caves and mountaintops to coastlines and houses

Open guide
A Chilean rose tarantula (Grammostola rosea) photographed from above, showing its dense grey-blue and brown urticating hairs, robust body, and eight legs resting on dark substrate.
Varies by species

Invertebrates

T

Tarantula

Family Theraphosidae

Ancient, gentle giants — the world's mightiest spiders are more at risk than most people realise.

Americas · Africa

Open guide
Female wolf spider carrying a round white egg sac attached to her spinnerets on sandy ground
Family page

Invertebrates

W

Wolf Spider

Family Lycosidae — over 2,900 described species worldwide

The spider that carries its egg sac on the spinnerets — then carries the spiderlings on its back.

Worldwide except Antarctica · Lawns, heath, coast, deserts and forest floors

Open guide

Conservation: what this group faces

Arachnids are mostly predators that suppress insects. Killing every spider in a house removes a free pest control service; habitat loss removes the specialists whose status is barely monitored.

Fund invertebrate & habitat protection Current appeals

Arachnids: frequently asked questions

Is a spider an insect?
No. Spiders are arachnids with eight legs and two main body regions. Insects have six legs and three body regions.
What is a daddy longlegs?
In Britain the name often means a harvestman (Opiliones), which is an arachnid but not a spider. Elsewhere it can mean a cellar spider — a true spider.
Are daddy longlegs the most venomous spiders?
No. Harvestmen are not spiders and lack venom glands of that type. Cellar spiders are not among the most medically significant species.
Which spiders are dangerous?
A small set of genera — including some widows and recluses — can cause medically significant bites. Most of the world’s spider species are not dangerous to healthy humans.
Do scorpions bite or sting?
They sting with a telson at the end of the tail. The pincers grab prey; venom is delivered by the sting.
Are arachnids endangered?
Many are poorly assessed. Habitat specialists and island endemics can be threatened even when common garden spiders remain abundant.

Other types of invertebrates

All invertebrate guides Animals A–Z