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Tick

Ixodida

Ticks are ectoparasitic arachnids belonging to the order Ixodida under the superorder Parasitiformes. They are extremely resilient arthropods that feed solely on vertebrate blood, often acting as a vector for transmitting pathogens, such as bacteria, viruses, and protozoans, to the host’s body and causing infectious diseases. 

About 900 known tick species are divided into 23 genera and three families: Ixodidae (Hard Ticks), Argasidae (Soft Ticks), and Nuttalliellidae.

Description

General Body Plan

They lack proper segmentation of their abdomen (or opisthosoma), which, like mites, are fused to their cephalothorax (or prosoma). Like other chelicerates, the tagmata has developed into two main parts: 

1. Gnathosoma (Head)

It contains the mouthparts comprising the feeding apparatus with the two palps, two chelicerae, and a hypostome.

The chelicerae are specialized appendages used for cutting and puncturing the skin, while palps are leg-like appendages that are sensory in function. On the other hand, the hypostome, adapted for piercing and sucking, helps anchor the tick’s mouthparts firmly onto the host’s skin.

2. Idiosoma (Body)

This part contains the walking legs, digestive tract, and reproductive organs. The ventral side of the idiosoma has sclerites (hardened plates) and a gonopore between the fourth pair of appendages. While nymphs and adults bear eight legs, the larval forms hatch with six legs, acquiring the other two only after molting into the nymph stage.

All three families have some distinct anatomical features that set them apart from each other.

Hard Ticks

Soft Ticks

Nuttalliellidae

Taxonomy

These arachnids are placed under the Superorder Parasitiformes, within which they are most closely related to Holthyrida, a small order of mites. Among almost 900 species, the majority (over 700) belong to the family Ixodidae. The family Nuttalliellidae, named after the bacteriologist George Nuttall, is monotypic, with the species Nuttalliella namaqua.

Ticks (Ixodida)

Distribution

Although ticks are cosmopolitan in distribution, they thrive better in warm, humid climates, given the optimum temperature and moisture required for their metamorphosis.

Habitat

These arachnids inhabit shadowy environments with leaf litter, especially those with an overstory of trees or shrubs. They also prefer ‘ecotones,’ the transitional habitat between woodlands and open areas.

While hard ticks typically reside on the host, soft ticks do not have a fixed dwelling and keep switching between sand, crevices, burrows, or buildings.

Diet

They are obligate hematophages that exclusively feed on vertebrate blood for survival.

Behavior

Lifespan

They may survive up to three years, depending on the species.

Reproduction and Life Cycle

All three families of ticks go through the same four stages in their life cycle: egg, larva, nymph, and adult. 

Hard Ticks

Depending on the species, they can possess a one-host, two, or three-host life cycle.

Soft Ticks

Unlike Ixodids, Argasid ticks may go through up to as many as seven nymphal stages. Mating and egg-laying typically occur away from the host in a secure environment. After hatching, larvae feed on a nearby host for several hours to days, dropping off the host and molting into their first nymphal instars. These nymphs seek out and feed on their second host (often the same as the first host) within an hour. This feeding is repeated until the last nymphal instar is reached, allowing the tick to molt into the adult form.

Nuttalliellidae

Nuttalliella namaqua is thought to have multiple hosts, though very little is known about its life cycle.

Predators

Natural predators of ticks include birds, small mammals like opossums, insects, nematodes, and predatory mites.

Adaptations

  1. Depending on the species, tick saliva contains around 1,500 to 3,000 anti-inflammatory proteins, called evasins, that allow them to feed on blood for about 8 to 10 days without the host noticing their presence.
  2. The tarsus of a tick’s first pair of legs contains Haller’s organ, a sensory structure crucial for detecting host odors, chemicals, temperature changes, air currents, and even infrared light emitted by their warm-blooded hosts.
  3. The cuticle of Ixodids can enlarge as their weight increases during their feeding stage by 200 to 600 times compared to their pre-feeding weight.

Interesting Facts

  1. Due to their slow metabolism during dormancy, an adult tick can go without food for a year or up to 430 days. During drought conditions, they can survive up to eighteen weeks without feeding.
  2. Surprisingly, ticks can survive in vacuum-like conditions for as long as half an hour.
  3. The oldest known tick fossils are those of a bird tick from the Late Cretaceous Period (94 to 90 million years ago). Several ticks from the genera Khimaira and Deinocroton were also unearthed from Burmese amber in Myanmar.

References Article last updated on 9th April 2024
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