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General Morphology

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Soft Ticks

The family Argasidae comprises 5 genera and approximately 170 species.
The 5 genera are: Argasinae (e.g. Argas reflexus, A. vespertilionis), Ornithodorinae (e.g. Ornithodorus hermsi, O. coriaceus, O. moubata), Otobinae (e.g. Otobius megnini), Antricolinae, Nothoaspinae.

The soft ticks have an oval or pear-shaped outline with the anterior body region broadly rounded. The mouthparts are difficult to see from a dorsal view. The soft ticks are inornate and have a granulated leathery appearance.

Soft ticks feed for short periods of time on their hosts, varying from several minutes to days, depending on such factors as life stage, host type, and species of tick. The feeding behaviour of many soft ticks can be compared to that of fleas or bedbugs, as once established, they reside in the nest of the host, feeding rapidly when the host returns and disturbs the contents. The outside surface, or cuticle, of soft ticks expands, but does not grow to accommodate the large volume of blood ingested, which may be anywhere from 5-10 times their unfed body weight.

They lack the scutum and have a leathery cuticle. But most species bear a centrally located dorsal plate which is covered by tiny mammillae, ridge structures that protrude above the cuticle surface. Subcircular depressions termed discs, representing sites of muscle attachment, occur in characteristic patterns over the dorsal and ventral surface.

In the larvae, an oval dorsal shield is usually present, but this structure should not be confused with the ixodid scutum, which always located on the anterior part of the body. In adults and nymphs, the capitulum is recessed ventrally, subterminal, hidden from a dorsal view.

Eyes, when present, occur on the lateral surface of the body. The ventral organ of unknown function appears as a broad transverse ridge posterior to the anus .

The spiracles occur on the supracoxal folds between the coxae of leg III and IV.

Male and female dimorphisms distinguish only by the appearance of the genital pore.

During their blood meal argasid ticks can increase their body weight 3-5 times because their highly folded integument allows extensive stretching without additional growth.

Figure 2: SEM-micrograph of argasid ticks; dorsal and ventral view.
Note the mouthparts only easily visible from the ventral side.

   

Further information

  • Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford University Press, New York

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