What does a typical encephalitic tick look like? - briefly
Encephalitic ticks, exemplified by Ixodes ricinus, are oval arachnids measuring 2–5 mm when unfed, with a reddish‑brown dorsal surface and a lighter ventral side. They have eight legs and a hard scutum covering the dorsal area of females.
What does a typical encephalitic tick look like? - in detail
A tick capable of transmitting encephalitic viruses is generally a hard‑tick (family Ixodidae). The dorsal surface is covered by a rigid scutum, a shield‑like plate that varies in color from reddish‑brown to dark brown depending on species and feeding stage. In an unfed adult, the scutum occupies most of the back; in females, engorgement expands the abdomen, creating a noticeable bulge while the scutum remains a fixed size.
Key morphological features include:
- Capitulum: located on the ventral side, bearing the chelicerae and hypostome. The hypostome bears backward‑pointing barbs that facilitate attachment.
- Eyes: most encephalitic vectors possess a pair of simple eyes (ocelli) on the dorsum, useful for distinguishing them from deer ticks (which lack eyes).
- Anal groove: a groove extending from the anus toward the posterior margin of the scutum; its presence confirms the specimen belongs to the Ixodes genus.
- Legs: eight legs, each ending in a claw with a pulvillus (a pad) that aids in gripping the host’s skin. Leg length is proportionally longer in nymphs than in adults.
- Mouthparts: visible from the ventral view, the palps are elongated and spoon‑shaped, while the chelicerae are slender and curved.
Size ranges are species‑specific:
- Larvae: 0.5–1.0 mm, translucent, lacking a scutum.
- Nymphs: 1.5–2.5 mm, dark brown, scutum covering most of the dorsal surface.
- Adult females: 3–5 mm unfed; after feeding, the abdomen can swell to 10 mm or more, appearing pale and distended.
- Adult males: 2.5–4 mm, scutum covering the entire dorsum, abdomen remaining relatively flat.
Coloration typically shifts from a lighter, almost tan hue in unfed stages to a darker, almost black tone after a blood meal. The ventral side remains lighter, with the capitulum and palps often appearing ivory or pale yellow.
These characteristics collectively enable identification of ticks that serve as vectors for encephalitis, such as Ixodes ricinus (European castor bean tick), Ixodes scapularis (black‑legged tick), and Dermacentor andersoni (Rocky Mountain wood tick). Accurate recognition relies on examining the scutum, eyes, anal groove, and leg morphology under magnification.