Module 10: Veterinary Ectoparasites

Module 10.4: Common soft ticks in North America

Common soft ticks in North America

Soft ticks, members of the family Argasidae, are a distinct group of ticks known for their unique biological and behavioral characteristics, differentiating them from the more commonly known hard ticks (family Ixodidae). Unlike hard ticks, soft ticks do not possess a scutum (a hard shield) on their dorsal side, giving them a more leathery and flexible appearance. In the United States, soft ticks are less frequently encountered by the general public compared to hard ticks, but they are no less important due to their role in transmitting diseases and their impact on animal and human health. Common soft ticks in the United States include, Argas persicus (Fowl or Poultry Tick), Ornithodoros spp. (Relapsing Fever Ticks), and Otobius megnini (Spinose Ear Tick). In this section we will discuss only the Spinose Ear Tick.

The Spinose Ear Tick: A Unique Soft Tick

Among the soft ticks, Otobius megnini, or the spinose ear tick, is particularly noteworthy. It is considered the most important soft tick in North America, primarily due to its widespread impact on domestic animals and livestock, especially horses and alpacas. This tick is unique in its parasitic behavior and lifecycle, making it a significant concern for animal health. Here is a video that discusses how cool they are!

Life Cycle of Otobius megnini (Spinose Ear Tick)

The spinose ear tick, Otobius megnini, has a unique and complex life cycle compared to other tick species as it is a one-host tick, meaning that the same host supports its parasitic stages. It primarily infests the ear canals of its hosts, causing significant irritation and potential secondary infections. Understanding its life cycle is crucial for effective management and control.

1. Egg Stage

  • Laying Eggs: Female spinose ear ticks lay their eggs in the environment, typically in sheltered areas such as cracks and crevices of buildings or under vegetation.
  • Number of Eggs: A single female can lay several hundred to over a thousand eggs at a time.
  • Incubation Period: The eggs hatch into larvae within about 3-5 weeks, depending on environmental conditions such as temperature and humidity.

2. Larval Stage

  • Appearance: The larvae are very small, six-legged, and have a spiny appearance that gives the tick its common name.
  • Host Seeking: After hatching, larvae actively seek out a host, often attaching to animals that come into contact with their hatching site.
  • Host Attachment: Larvae typically attach to the external ear canal of the host and begin feeding on blood and tissue fluids.
  • Feeding Duration: The larval stage can last several days to a few weeks while they feed, depending on the availability of a suitable host.

3. Nymphal Stage

  • Molting to Nymphs: After feeding, larvae molt into nymphs, a process that occurs while they are still attached to the host.
  • Appearance: Nymphs have eight legs and are larger than larvae. They maintain the spiny appearance characteristic of this species.
  • Host Continuation: Nymphs continue to feed on the host’s ear canal. This stage can be particularly irritating and cause significant discomfort to the host.
  • Feeding Duration: The nymphal stage lasts several weeks to several months, during which time the nymphs may take multiple blood meals.

4. Adult Stage

  • Leaving the Host: Unlike many other tick species, the adult Otobius megnini does not feed on the host. After completing their nymphal stage and final molt, they drop off the host and live in the environment.
  • Appearance: Adult ticks are relatively large and lack the spiny appearance of the nymphs.
  • Reproduction: Adult ticks focus on reproduction. Females lay eggs in the environment, continuing the life cycle.
  • Lifespan: Adults may live for several months to a year in the environment, depending on conditions, but they do not feed during this time.

Impact and Management

The spinose ear tick poses a significant challenge due to its ability to infest all domestic animals and its particular nuisance to livestock. Its presence in the ear canal can cause severe discomfort and health complications, such as otitis externa and secondary bacterial infections. Effectively managing this tick involves understanding its lifecycle, host interactions, and environmental preferences.


Otobius mengnini (spinose ear tick)
Otobius mengnini (spinose ear tick)

Key Features of Otobius megnini:

  • Host Specificity: The spinose ear tick is a one-host tick, meaning that the same host supports its parasitic stages.
  • Lifecycle: The larval and nymphal stages are parasitic and inhabit the ear canal, where they feed and develop. Upon maturity, the nymphs detach from the host to molt into adults, which live and reproduce in the environment.
  • Morphology: Unlike hard ticks, Otobius megnini lacks a scutum. Despite this, it is armed with thousands of small spines across its body, classifying it as a soft tick.

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