Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada

FOR REVIEW: Measurement

  1. Accuracy and Precision
    These aren't the same thing:
    Precision is how much detail is specified as to the exact size of the thing measured.
    Accuracy is how well the measurement matches the real size of the thing measured.
    For example, if a bug is actually 12.1357 mm, then saying it's 13.927 is more precise than saying it's 12 mm, but 12 mm is more accurate.
    Our goal should be accuracy
  2. How to measure, by classification:
    In general, ignore things that stick out, like legs, mouthparts, and antennae.
    Spiders- front of the cephalothorax to tip of the abdomen
    Insects- front of the head to the tip of the abdomen.
    Dermaptera- Earwigs: front of the head to the base of the forceps
    Exception: moths and butterflies are often measured from wingtip to wingtip with the wings fully open.
  3. Metric Size-Guesstimation Chart
    The idea is to give the equivalent in metric units for American non-metric measurements and the sizes of familiar objects of known size one is likely to have handy. In those cases where a range is given ("about..."), that's the lower and upper limits of what would be described by that value.
    1 foot: 30.5 cm (about 25-36 cm)
    US dollar bill,etc. (long way): 156 mm
    6 inches 15.24 cm: CA banknotes (long way)
    5 inches 127 mm
    4 inches 101.6 mm
    Credit card (long way) 85.6 mm
    3 inches 76.2 mm
    CA banknotes (narrow way) 69.85 mm
    US dollar bill,etc. (narrow way) 66.3 mm
    Credit card (narrow way) 54 mm
    2 inches 50.8 mm
    US Kennedy half-dollar coin 30.6 mm
    CA 2-dollar-piece (Toonie) 28 mm
    CA 50-cent-piece/half-dollar 27.13 mm
    CA dollar coin (Loonie) 26.5 mm
    1 inch 25.4 mm (about 19-32 mm)
    US quarter 24.3 mm
    CA quarter 23.9 mm
    7⁄8 inch 22.2 mm (about 21-23 mm)
    Nickel (US & CA) 21.2 mm
    Penny (US & CA) 19.1 mm
    ¾ inch 19 mm (about 16-22 mm)
    CA dime 18 mm
    US dime 17.9 mm
    5⁄8 inch 15.9 mm (about 15-17 mm)
    ½ inch 12.7 mm (about 10-15 mm)
    3⁄8 inch 9.5 mm (about 8-11 mm)
    ¼ inch 6.4 mm (about 3-9 mm)
    1⁄8 inch 3.2 mm (about 2-4 mm)

I prefer no-kill, usually hands-off images for natural posture, etc. Thus capturing a wingspan is usually not possible. My aim with measurements is to ballpark a size for aiding in identification. Other qualities are used for species id if possible. So for a moth resting in a wings-folded position, a wing leading edge length is possible. This allows me to guess other parameters, as a coarse filter (e.g. a 15mm forewing leading edge length would mean my moth is probably not one who typically has a 12-18 mm wingspan.) I specify what i am measuring (e.g. FW length 15mm). Hope that is helpful.

Measuring Orthoptera
I'm measuring Orthoptera, more specifically Acridiae. How would you go about measuring them properly. I usually do two measurements, body length from head to abdomen tip and wing length from the farthest thorax attachment to the wingtips. Yet some species have wingtips extending past the abdomen so are my measurements inaccurate?

"Apparent Body Length",
often abbreviated ABL, is defined (at least in the ground beetle literature) to be the distance from mandible tip to elytron tip. However, in cases where the abdomen extends well beyond the elytra (lebiines, brachinines), one measure to the abdominal apex.

metric unit abbreviations seem to be conventionally used w/o the period -- just km, mm, kg, l, &c.

I measure
wasps by their wingspans when they are my spread specimens.