Insect Anatomy and Metamorphosis

External Anatomy of Insects

• Orders
  • 9-10 major orders of insects.
  • Each order exhibits adaptations that help define it.

Types of Metamorphosis in Insects

• Three Types of Metamorphosis:

  • Ametabolous (No Metamorphosis):

  • Juveniles resemble tiny adults.

  • Examples:

    • Collembola (Springtails): Tiny, wingless; equipped with a furcula for jumping; found in soil, leaf litter; feed on fungi and decaying matter.
    • Diplura (Bristletails): Long cerci (tails); no eyes; inhabit moist soil; act as scavengers/predators.
    • Zygentoma (Silverfish): Flat, silvery; possess 3 tail filaments; usually found indoors or under rocks, feed on starches.

  • Hemimetabolous (Incomplete Metamorphosis):

  • Nymphs resemble adults and typically share similar habitats.

  • Examples:

    • Ephemeroptera (Mayflies): Characterized by 3 long tail filaments; aquatic nymphs filter feed; short-lived adults.
    • Odonata (Dragonflies/Damselflies): Large eyes, strong wings; gilled aquatic nymphs act as aquatic predators; adults are aerial hunters.
    • Plecoptera (Stoneflies): Soft bodies with 2 cerci; indicate good water quality; inhabit cold, oxygen-rich streams.
    • Hemiptera (True Bugs): Possess piercing-sucking mouthparts; feed on plants; utilize camouflage and mimicry for survival.
    • Orthoptera (Grasshoppers and Crickets): Notable hind legs for jumping; skilled at sound production; found in grasslands; employ camouflage and herbivory.
    • Blattodea (Cockroaches): Flat bodies, long antennae; known for being fast runners; nocturnal scavengers, highly resilient.
    • Mantodea (Mantids): Equipped with raptorial forelegs; act as sit-and-wait predators; excellent camouflage.

  • Holometabolous (Complete Metamorphosis):

  • Involves distinct life stages: larva → pupa → adult; larvae often occupy different environments than adults.

  • Examples:

    • Diptera (Flies): Possess one pair of wings and halteres; have sponging/sucking mouthparts; larvae thrive in decaying matter or water.
    • Lepidoptera (Butterflies, Moths): Characterized by scaled wings; coiled proboscis; larvae (caterpillars) feed on vegetation; adults are nectar feeders.
    • Coleoptera (Beetles): Feature hardened wing covers (elytra); have chewing mouthparts; represent the most diverse group exploiting various food sources.
    • Hymenoptera (Bees, Wasps, Ants): Have two wings; possess chewing and sucking mouthparts; are critical pollinators and exhibit social behavior as colony builders.

Other Arthropod Classes Not Included in Insect Orders

• Arachnida (Spiders):
  • Characteristics: 8 legs, no antennae, two body parts; utilize webs, venom, and ambush tactics for survival.
• Malacostraca (Pill Bugs):
  • Seven pairs of legs; segmented bodies; able to roll into a ball; prefer moist environments.
• Chilopoda (Centipedes):
  • Possess one pair of legs per segment; fast predators equipped with venomous claws.
• Diplopoda (Millipedes):
  • Have two pairs of legs per segment; move slowly; secrete chemicals as a defense mechanism.