The nature of feather construction
|Peacock herl - actually barbs - showing the difference between lower/proximal (here to the left) and upper/distal barbules.
Birds have a tremendous variety of combinations of feather components. For instance the Crowned Crane crest feathers are each made up of a short quill, a twisted rachis, and few barbs. What the fly tier considers the useable portion of a typical cocks hackle in a dry fly has few or no barbules on the barbs since those barbs with barbules are stripped prior to application.
Fly tiers somewhat incorrectly refer to this part of the feather as being the web or webby portion of the feather. Web is a term synonymous with the whole vane.
Some feathers have barbules without barbicels. Examples would include peacock upper tail covert feather barbs below the eye
as well as down feathers from any bird. (When considering peacock herl,
the barbs are often mistakenly referred to as quills.
The barbules also are confusingly referred to as herl
for example where the fly pattern for a Quill Gordon calls for a quill body
that requires the removal of the herl
from the barb. In actuality, the quill
is a barb and the herl
referred to are barbules on the herl or barb.) Barbicels are found on flight feathers (i.e., turkey tail feathers, peacock secondary wing feathers, etc.) with the exception of flightless birds (i.e., emu, ostrich, kiwi, etc.) Just as a barb does not necessarily have barbules, barbules do not necessarily have barbicels. Turkey marabou
(semi-plume) is an example of a feather with barbules, but no barbicels. Body (contour) feathers of most pheasants are examples of feathers having barbules without barbicels (plumulacious vane) on some barbs and barbules with barbicels (pennaceous vane) on others.