Hard Ticks

Overview

The family Ixodidae is by far the largest and economically most important family with 13 genera and approximately 650 species¹.

The most important species in North America are Ixodes pacificus, Ixodes scapularis (dammini), Ixodes ricinus, Dermacentor variabilis, Rhipicephalus sanguineus, Amblyomma americanum, Haemaphysialis leporispalustris, Boophilus annulatus and Boophilus microplus.

The main attribute of this family is a plain dorsal scutum or shield, that distinguish these ticks from other families. This sclerotized plate covers the entire dorsal surface of the male, but only one third of the females dorsal surface. The size of the scutum remains constant during the feeding of the female. During its engorgement it covers a smaller part of the body².

The folded cuticle posterior the scutum constitutes the alloscutum. However, females, nymphs and larvae, with a more limited scut covering, may become greatly distended when engorging a huge blood meals. The scutum limits the expansion of the body of the male ticks.

In all ixodid ticks, the palps contain 4 segments, the tiny terminal (4th) segment (with sensory sensillae) is retractable and found in a cavity on the ventral surface of segment III.
The mouthparts include the paired chelicerae, the segmented palps, and the ventrally situated, toothed hypostome, all mounted on the basis capituli1, 5.

Fig. SEM-micrograph of mouth parts of ixodid ticks.
A view from the dorsal side in a larva of Ixodes ricinus. x 150.
B View into the mouth (M) of Amblyomma variegatum. Note the teeth at the hypo- and epistome. x 400. C, chelicera; M, mouth; P, pedipalps

Eyes, if present, occur on the postero-lateral margins of the scutum.
Characteristically, the capitulum of hard ticks is visible from a dorsal view. They can be easily differentiated by the shape of the basis capitulum and by the former of anal grooves.

Fig.: Diagrammatic representation of an ixodid tick (e.g., Dermacentor sp.) from its ventral side. AN, anus; CH, chelicera; CL, claw; CS, sheath of chelicera; CX, coxa; E, esophagus; EM, pulvillus; FE, festoon; GN, gnathosoma (capitulum); GO, genital opening; H, hypostome; PP, pedipalpus; SA, salivary duct; SC, scutum; STI, stigma; TA, tarsus.

The peritreme or groove is big and clearly visibly around the stigmal plate. Grooves are deep, linear depressions in the body cuticle, usually on the ventral surface.
Also typical is a strong build hypostome with robust teeth. They work as barbs, so it is impossible for the tick to detach spontaneously. This led to the name of the family (greek: Ixos = glue)³.
The Pedipalpus is constricted with the tibia and only some hairs may be visible.
A pair of areae porosae, clusters of small pores, is found on the dorsal surface of the basis capitulum. Its secretions prevent oxidation of unsaturated lipids coating the eggs. Pad-like pulvilli on the praetarsi of the walking legs do exist, while the coxal gland is absent⁴.