Kingdom - Animalia

Phylum - Arthropoda

Subphylum- Chelicerata

Class - Arachnida





From microscopic mites to the nearly half pound Goliath birdeaters of South America, arachnids come in a range of sizes.

 Arachnids have:

  • two tagmata (distinct body regions):
    • prosoma or cephalothorax (head and chest combined)
    • opisthosoma (abdomen).
  • no antennae.
  • no wings.


 There are approximately 100,000 known species of arachnids in 11 orders


Illinois has known representatives of 5 of those orders:

Order Araneae - Spidersspider.png

Spiders have:

  • a cephalothorax and an abdomen.
  • spinnerets to produce silk.
  • pedipalps ("mini-legs") in front of mouth, used to grab prey.
  • fangs to bite prey.
  • most have venom glands.
  • 650 species in Illinois.

Order Acari: Mites & Ticks

The Acari have:tick.png

  • two tightly connected tagmata appearing as one unit.
  • lost the eyes of many species.
  • modified chelicerae for piercing, sucking, or biting.
  • 20 species of ticks and ~10,000 species of mites in Illinois.

Order Scorpiones: scorpionsscorpion.png

Scorpions have:

  • eight legs
  • chelate (pincer-like) pedipalps
  • narrow tail with venomous stinger
  • one Illinois species

Order Opiliones: Harvestmen or Daddy long-legsdaddylonglegs.png

Harvestmen have:

  • small round bodies.
  • the two tagmata are tightly connected, appearing as one unit.
  • long thin legs.
  • pedipalps to hold food.
  • no venom glands.
  • 19 species in Illinois.
  • one pair of eyes.

Order Pseudoscorpionida: Pseudoscorpionspseudoscorpion.png


  • are small (2-8 mm)
  • have chelate (pincer-like) pedipalps
  • lack the long tail of a scoprion
  • are found in all terrestrial habitats
  • have 28 species in Illinois