How old are lice? - briefly
Lice have been present since the Cretaceous period, roughly 100 million years ago, as shown by fossilized specimens. Modern species retain the same basic morphology, indicating a long‑standing evolutionary stability.
How old are lice? - in detail
Lice belong to the order Phthiraptera, a lineage that arose alongside the diversification of birds and mammals. Fossil specimens preserved in amber date to the middle Eocene, roughly 35 million years ago, confirming the presence of both chewing and sucking forms at that time. Molecular‑clock analyses, calibrated with these fossils, extend the origin of the clade to the Cretaceous, approximately 70–100 million years ago, when the first modern avian and mammalian hosts appeared. Consequently, most extant lice species trace their ancestry to divergences that occurred millions of years before the emergence of Homo sapiens.
Individual parasites have a short biological life span. On human hosts, adult body lice (Pediculus humanus humanus) survive for 30 days on average; head lice (Pediculus humanus capitis) live 20–30 days. On birds, the lifespan of a typical chewing louse (e.g., Philopterus spp.) ranges from 10 to 20 days, while sucking lice (e.g., Menacanthus spp.) persist for about 15 days. The life cycle comprises:
- Egg (nit): incubation period 7–10 days, depending on temperature and host species.
- Three nymphal instars: each molt occurs after 2–4 days, with the entire nymphal phase lasting 6–12 days.
- Adult stage: reproductive period begins shortly after the final molt and continues until death.
Reproductive output is high; a single female can lay 5–10 eggs per day, producing 100–300 offspring over her lifetime. This rapid turnover, combined with host‑specific coevolution, explains the extensive species diversity observed today—over 5,000 described taxa, each adapted to a particular host lineage that has itself evolved over tens of millions of years.
In summary, lice as a taxonomic group originated in the Cretaceous, roughly 70–100 million years ago, while individual parasites live for only a few weeks, completing their development from egg to adult within a month under optimal conditions. The long evolutionary history of the clade contrasts sharply with the brief existence of each organism.