Arthropod Identification Laboratory — Specimens and Microscopy

Why Arthropod Identification Matters in Pest Control

A pest control technician cannot treat what they cannot name. Choosing the wrong pesticide, the wrong formulation, or the wrong application site is costly, sometimes illegal, and occasionally dangerous. Accurate identification to order — and ideally to species — drives every decision that follows: product selection, label compliance, inspection strategy, and client communication. This laboratory session builds the core skill: using magnification tools and a dichotomous key to produce a defensible, documented identification.

Safety Before You Touch a Specimen

All preserved arthropod specimens in this lab are stored in or have been rinsed with 70% ethanol. Ethanol is flammable — keep it away from open flames and hot surfaces. Wear nitrile gloves whenever you handle specimens, ethanol, or prepared slides. Safety goggles must be on before you open any specimen container. Do not eat, drink, or touch your face during the lab. Forceps and dissecting needles have sharp tips; point them away from your body and your neighbors. If you break a glass slide, do not pick up fragments with bare hands — use a brush and dustpan. Any PPE violation noted by the instructor requires you to repeat that segment of the lab before you can receive sign-off.

The Compound Microscope: Quick Setup Review

Start on the lowest-power objective (typically 4× or 10×). Place your prepared slide on the stage, secure it with the stage clips, and use the coarse-focus knob to bring the image into rough focus while watching from the side — not through the eyepiece — to avoid driving the objective into the slide. Then look through the eyepiece and fine-focus. Increase magnification only after you have a clear low-power image. At high power, use the fine-focus knob only.

Total magnification equals the objective power multiplied by the eyepiece power. A 10× eyepiece on a 40× objective gives 400× total. Always record the magnification used on your sketch.

Wet-Mount Slide Preparation

To examine a small appendage — a leg segment, antenna, or mouthpart — place the structure in a drop of 70% ethanol on a clean glass slide. Lower a coverslip at a 45-degree angle to minimize air bubbles. Use a dissecting needle to gently position the appendage before the coverslip traps it. Wipe any excess liquid from the edges of the slide before placing it on the microscope stage.

Using the Ocular Micrometer for Measurement

Many compound microscopes have an ocular micrometer — a ruled scale etched into one of the eyepieces. Before measurements mean anything, the ocular scale must be calibrated with a stage micrometer (a slide with a scale of known length). Once calibrated, you can measure body length or feature width directly. Record your measurements in millimeters and include a scale bar on every sketch.

Hand Lens Technique

For whole specimens too large for a slide, use a 10× hand lens. Hold the lens close to your eye, then bring the specimen up to the lens until it comes into focus — not the other way around. Good lighting is essential; angle a lamp so light rakes across the specimen surface to reveal texture and color patterns.

Reading a Dichotomous Key

A dichotomous key presents a series of paired, mutually exclusive choices (couplets). At each couplet you choose the statement that best describes your specimen, then follow that lead to the next couplet or to a final identification. Work methodically:

1. Start at couplet 1.

2. Read both choices completely before deciding.

3. Record the couplet number and your choice in your lab log — this is your key pathway.

4. If you reach an identification that does not look right, back up one couplet and try the other lead.

Common mistakes include skipping couplets, guessing at ambiguous features without magnification, and confusing leg count for similar-looking groups. Non-insect arthropods trip up many beginners: spiders have eight legs and two body regions (cephalothorax and abdomen), mites and ticks also have eight legs as adults, millipedes have two pairs of legs per body segment, and sowbugs (isopods) are crustaceans with seven pairs of legs.

Documenting Your Identification

Your lab log entry for each specimen must include:

• Specimen number and a clear pencil sketch with scale bar and magnification noted
• Key pathway (couplets followed, choice made at each)
• Order (e.g., Araneae, Coleoptera, Diptera)
• Common name (e.g., wolf spider, ground beetle, house fly)
• Two diagnostic features — observable characteristics that distinguish this taxon (e.g., "three body regions, six legs, one pair of wings" for Diptera)

Neat, complete records are not optional. Both the state pesticide applicator license exam and NPMA certification assess pest identification knowledge, and the habit of precise documentation protects you professionally in the field.

Peer Verification and Error Analysis

After the independent identification round, you will exchange trays with a classmate and re-key three specimens independently. Discrepancies are valuable learning moments — not failures. When the instructor reviews the answer key, pay close attention to the misidentifications most likely to affect field decisions, such as confusing a sowbug (non-target crustacean, generally not treated) with a pillbug, or misidentifying a beneficial ground beetle as a pest species.