Lice Life Cycle: Introduction to Lice, Stages in the Lice Life Cycle, the Egg (For CBSE, ICSE, IAS, NET, NRA 2022)

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Introduction to Lice

  • Louse (plural: lice) is the common name for members of the order Phthiraptera.
  • Lice were ubiquitous in human society until at least the middle ages.
  • They contain 5,000 species of wingless insect.
  • They are obligate parasites living externally on warm-blooded hosts.
  • This includes every species of bird and mammal, except for monotremes, pangolins, and bats.
  • They are vectors of diseases such as typhus.
Head Louse

Life Cycle Stages

Life Cycle Stages

Stage 1

The Egg

  • The eggs are tiny particles and known as nits.
  • The egg can measure up to 0.8 mm, oval-shaped and yellow or white colored.
  • It takes around one week at least for the egg to hatch into nymphs.

Stage 2

The Nymph

  • Lice undergo three stages of moulting.
  • These are the tiny versions of lice.
  • It is yellow to white colored.

Stage 3

The Adult

  • The adult lice measure up to 2 mm in length.
  • The life span of adult lice is 30 days that too if it is fed frequent blood meals on a regular basis.

Evolution

Anoplura

  • Sucking lice
  • Occurring on mammals exclusively.

Rhynchophthirina

Parasites of elephants and warthogs.

Ischnocera

  • Mostly avian chewing lice.
  • One family parasitizes mammals.

Amblycera

  • A primitive suborder of chewing lice.
  • Widespread on birds.
  • They live on South American and Australian mammals as well.

Other Important Points

  • Humans host two species of louse namely the head louse and the body louse.
  • The body louse has the smallest genome of any known insect.

Chewing lice:

  • Live among the hairs or feathers of their host.
  • Feed on skin and debris.

Sucking lice:

  • Pierce the host՚s skin.
  • Feed on blood and other secretions.

They usually spend their whole life on a single host.

Colour of the Lice:

  • Usually cryptically colored.
    • To match the fur or feathers of the host.
    • Colour varies from pale beige to dark grey.