The larvae of C. incisa and C. pygmaea are easily discriminated. The opposite hold for their puparia, which is unfortunate because they are found frequently (much more often then the larvae) and because they are quite conspicuous. They are deep black with a strong violet or blue metallic shine; they are lying in the mine, not in pupal chamber, but anchored to the inner wall of the mine by means of a thread. Often several puparia are found together, and then frequently the anchor wires are fused near the point where they are attached to the plant.
De Meijere (1928) and Hering (1957a) state that the distal margin of the common base of the rear puparia is straight or convex in incisa, concave in pygmaea. This must be related to the size of the “warts” at either side of the rear spiracula, small in incisa, large in pygmaea. In practice, however, I find this character difficult to use. A second character invoked by them is that the intersegmental constrictions in incisa are roughened by tiny scalelike irregularities, while those in pygmaea have minute transverse corrugations. I have the impression that this is not reliable.
Phalaris arundinacea, ‘t Twiske; the anchor wire is unusually short
first part of tha anchor wire; how the thread is formed exactly, and its composition are unknown to me