Nymphs resemble the adult tick in that they have eight legs. They do not, however, have a genital opening. Nymphs must be able to live without feeding for long periods of time until it finds a suitable host.
Hard ticks have only one nymphal instar while soft ticks may have several. A few ticks have only one host and molt on it, leaving the host only to lay eggs.
Ixodid nymphs commence questing and the entire cycle of host contact, attachment, feeding, engorgement, and detachment is repeated.
Detached engorged nymphs drop off, ecdyse in the natural environment, and the engorged nymphs molt into unfed adults.
Several variations of this general ixodid developmental pattern exist. In some species, fed larvae remain on the host, molt in situ, and the unfed nymphs reattach. Only following their engorgement do the nymphs detach. Then, they molt off the host to the adult stage. These ticks are known as 2-host ticks.
A more extreme modification occurs in the winter tick Dermacentor albipictus or the cattle tick Boophilus microplus and other Boophilus species.
In these species, all stages remain on the host after the larvae attach. Only the fed, mated females drop to oviposit in the natural environment. These ticks are termed 1-host ticks.
Following engorgement argasid fed larvae detach, drop off and ecdyse, molting into the first nymphal stage (N1). Hungry N1 nymphs again attack hosts that enter the niche, repeating the cycle.This cycle of host contact, rapid feeding, engorgement, detachment and ecdysis in the niche occurs several times.
There are often many nymphal molts in the life cycle. Fed larvae molt to first stage nymphs (N1) resembling miniature adults in body characteristics, but lacking the genital pore and any evidence of sexual dimorphism. The fed nymphs molt again to yet another nymphal stage, N2 and cycle of host seeking, feeding and molting is repeated. In some species, 5, 6 or even 7 nymphal molts occur before the ticks mature to adults.
The highest recorded number of nymphal stages is 8 (Hoogstraal, 1985). The number of nymphal states is not consistent, even within the same species. Nutritional factors, especially blood volume taken in previous stages, is believed to be an important indicator of the number of nymphal stages.
Moreover, males usually emerge sooner than females, i.e., males require 1 or 2 fewer nymphal stages than do females.
In the Argasidae, the passage of so many nymphal stages contributes to a much longer life cycle than in the Ixodidae. In addition, many argasid ticks can resist long periods of starvation during their development, so that the life cycle can be extended for many years.
After finding a host and feeding, the nymph molts and becomes an adult tick.
- Hoogstraal H: Argasids and nuttalliellid ticks as parasites and vectors. Adv Parasitol. 1985, 24, 135-238
- Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford University Press, New York