North American dragonflies vary greatly in size, from about 1 inch to almost 6 inches
long. Correctly estimating the size is important in identification.
Some books express length in inches, others in millimeters, and some use both.
Length refers to the measurement from the "nose" to the "tail tip."
Another measurement that may be seen is the length of the wing, especially relative
to the length of the abdomen.
Actual size on a monitor can vary but the size difference between the 3.3"
Dragonhunter and the 1" Little Blue Dragonlet (both females) is accurately
represented in this composite. While these aren't America's biggest and smallest
Dragons, they're pretty close.
How do you know the exact size of the Dragon you are looking at? If you are
holding it, it's pretty easy to measure it, but when you are watching a free-flying
Ode, it can be pretty hard to figure out.
Comparison to other odes may be the easiest. Once you know 1 or 2 species,
look at your unknown bug and compare it to others that are nearby. Then you
can say "It's smaller than a skimmer" or "about the size of a Darner."
Another technique is to judge the Ode against something that can be measured.
If it is perched on a leaf, you can measure the leaf after the critter flies away.
Or you can compare it to the length of your hand or finger.
In flight, the height of the bug and the surroundings can play tricks. But
if it is real high up, you may never figure it out anyway!
Many field guides and manuals include the size. Some guides go a bit further
and include a ruler printed along the cover. A few even use bars or lines
to indicate the actual length of the insect. These are great if you are holding
the insect but can also help give a visual impression of the length.
VERY IMPORTANT: Remember that the lengths printed
are estimates of the average bug or ranges of size. In general, females are
larger than males although there are exceptions. Also species may have very large
and very small individuals.
For very precise in-hand measurements, you may need to purchase calipers.
These can be necessary for serious students who need to measure the exact width
of an abdomen or length of claspers. See our
equipment section for some help with this.