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Anatomy of a Female Deer Tick

Dorsal View

Hypostome

Barbed mouthpart injected into host to suck blood. Adult males will use the hypostome to fertilize adult females.

Palp

Used to detect a nearby host.

Porose area of Basis Capituli

Used as an identifying characteristic to determine tick species. Adult female deer ticks will have smaller porose areas than other tick species.

Scutum/Shield

Used as an identifying characteristic to determine tick life stage, species, and sex. Only nymph and adult female deer ticks will have shield located on the top portion of the back. Deer ticks have black, oblong shields.

Ventral View

Hypostome

Barbed mouthpart injected into host to suck blood. Adult males will use the hypostome to fertilize adult females.

Palp

Used to detect a nearby host.

Trochanter

Part of the leg that attaches to the coxa. Deer ticks will have trochanters without spurs. This characteristic can be useful in identifying tick species.

Basis Capituli

Attaches the mouthparts to the body. The basis capituli of a deer ticks will be straight at the bottom where it connects to the body and will be missing rounded humps on the top on either side of the hypostome. These characteristics are used in identifying the species.

Coxa I-IV

Attach the trochanter of the leg to the body of the tick.

Genital Aperture

Where the adult male tick will insert his hypostome to mate and fertilize the adult female tick.

Spiracular Plate

Has glands that may be involved in regulation of water loss and air diffusion. Used as an identifying characteristic to determine tick species.

Anal Groove

Used to identify species of tick. Deer ticks (Ixodes scapularis) will have an anal groove that extends above the anus while other species of tick not in the genus Ixodes will have an anal groove that stays below the anus.

Actual Size of the Adult Female and Nymph Deer Ticks

Actual size of an adult female deer tick and nymph deer tick

The adult female deer tick (left) is about .40cm long when measured from the tip of the mouthparts to the bottom of the abdomen. The nymph deer tick (right) is about .15cm long when measured from the tip of the mouthparts to the bottom of the abdomen.

Adult Female Deer Tick Engorgement

Female deer tick engorgement over time.
As adult females feed, their bodies become larger and their shields stay the same size. A scutal index can be used to estimate hours of engorgement by taking measurements of the width of the shield and the length of the body under a microscope.

Identifying Characteristics of an Adult Female Deer Tick

Contents

  1. Examining the Hypostome and Palps
  2. Examining the Basis Capituli
  3. Examining the Coxa and Trochanters of the Legs
  4. Examining the Scutum/Shield

When we receive a tick in the lab, the first thing we do is analyze it under a microscope. Using characteristics specific to the deer tick we can identify the species.

1. Examining the Hypostome and Palps

The palps of a deer tick are long and the hypostome has 4 rows of teeth-like projections on each side.

Denticle
Small, tooth-like projection; Individual, recurved teeth on the ventral side of the hypostome. Usually arranged in parallel, longitudinal rows or files.
Hypostomal Dentition
Arrangement or number of files of denticles on either side of the middle line of the hypostome.

Determining Hypostomal Dentition:

  • View hypostome under microscope
  • Count rows/files of denticles on either side of the middle line (See example below)
Adult Female I. scapularis Hypostome
Figure 1 — Adult Female I. scapularis Hypostome: If you count the rows of denticles on either side of the median line you see there are 4 rows on the left side of the middle line and 4 rows on the right side of the middle line. That means the Hypostomal dentition is 4/4 (4 rows of denticles on one side of the middle line and 4 rows of denticles on the other side of the middle line).
Palps

2. Examining the Basis Capituli

The basis capituli connects the mouth parts (hypostome and palps) to the body. When identifying a deer tick we look for a basis capituli that has a nearly straight bottom and is missing rounded humps on either side of the palp. We also look for small porose areas.

Basis Capituli
Porose Areas

3. Examining the Coxa and Trochanters of the Legs

The coxa is the part of the tick that connects the leg to the body. Ticks have four coxae and four legs. Deer ticks will have a spur on the first coxa (coxa I) that is not too long or short. They will also have smaller spurs on the 2nd, 3rd, and 4th coxa.

The trochanter is the part of the leg that connects to the coxa and body of the tick. Ticks have one trochanter per leg. Adult female deer ticks will be missing a spur on their trochanters.

Spur on Coxa I Spurs on Coxa II & III Missing Spurs on the Trochanter

4. Examining the Scutum/Shield

The scutum/shield rounded, not roughened and is smooth with very small punctations (spots).

Scutum/Shield

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