Analytical: How to Identify Medically Important Arthropods - Morphology

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The page below is a sample from the LabCE course Arthropods and the Clinical Laboratory. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Analytical: How to Identify Medically Important Arthropods - Morphology

Adult arthropod specimens are most frequently submitted to the clinical laboratory for identification; larvae are small and not as easily observed during the patient exam.
Whole specimens submitted to the clinical laboratory may not need to be identified to the genus and species level, depending on the arthropod in question. (For example, ticks should be identified to the species level, while it is not necessary for bedbugs to be identified to this level.)
Morphologic features are important in making an identification using:
  • Macroscopic observation
    • Take measurements (length and width) using a small metric ruler (mm or cm)
    • Observe for blood spots or red color inside the translucent abdomen
    • Record the types and numbers of body parts seen
  • Microscopic observation
    • Use of a light microscope (also called optical microscope) with an illumination source and different levels of magnification; ocular micrometer is useful if measuring small organisms
    • Use of a stereo microscope or dissecting microscope with low power and reflected light from the object
During the macro- and microscopic examinations, ask the following questions:
1. Is there a head, thorax, or abdomen? (Count the number of body parts.)
2. How would you describe the abdomen? (Tail present? Pinched waist? Are wings present? Do wings cover the abdomen? Are wings shorter than the abdomen?)
3. Are legs present? (How many pairs of legs?)
4. Do you see a pair of antennae? (How many segments?)
5. How many pairs of wings are present? (Membraneous? Or, leathery? Scales? Are the pairs similar or different?)
6. Are the mouthparts visible? (Retracted into the head? Or tubular? Sucking?)
7. Are body segments visible? (Does each segment contain a pair of legs? Or, two pairs?)
Basic IDAbdomen, MouthLegsAntennaeWings
Scabies, MitesTiny, rounded shape. Mouthparts directed anteriorly. Dorsal spines. Scabies burrows in skin.2 pairs anterior, 2 pairs posteriorNo true antennae, but palps and mouthparts/ suckers may be confused with antennae None
Bedbugs, Kissing BugsHead, thorax, abdomen; tubular mouth directed backward.3 pairs1 pair (four-segmented long antennae)Wings in kissing bugs, but reduced wings or pads in bedbugs
Lice Sucking mouthparts retracted into head.Claws attached to each leg; 3 pairs of legs1 pair (five segmented) None
Ticks Head and abdomen; oval body, saclike.4 pairs as adultsNone None