APPLICATION OF THE TRANSMISSION ELECTRON 
MICROSCOPE TO THE EXAMINATION OF 
SPIDER EXUVIAE AND SILK* 
By Rainer F. Foelix 
Lehrstuhl fur Zellphysiologie, Ruhr-Universitat Bochum 
D 4630 Bochum, West Germany 
In recent years the scanning electron microscope (SEM) has been 
used fruitfully to study the fine structure of many arthropods, 
including spiders. The advantage of the SEM lies in the simple 
method of preparation — no embedding and sectioning has to be 
done — and its large depth of focus, which yields almost three- 
dimensional views of surface structures. Drawbacks of the SEM 
are a limited resolution (1 50-200 A) and, as well, lack of availability 
to most researchers. The transmission electron microscope (TEM) 
has a much better resolution ( < 10A) than the SEM, but requires 
objects of less than o. 1-0.2 /x thickness to allow penetration of the 
electron beam. 
It was found that by simply mounting parts of spider exuviae 
(preferably of early instars) on Formvar-coated copper grids, details 
of hairs and claws can be seen with the TEM. If a leg tip of an 
exuvia is placed on a water droplet on the Formvar membrane, it will 
firmly adhere to the membrane after the water has evaporated. The 
preparation can then be viewed immediately in the TEM. Better 
stability and more contrast may be achieved by shadowing the speci- 
men at an angle of 40-50° with a metal (e.g. copper). The very 
delicate scopula hairs (Fig. 1-4) are especially well-suited for exam- 
ination with the TEM, but other hairs and bristles can also be easily 
surveyed and classified. For instance, the open tip of chemosensitive 
hairs (Foelix, 1970) is convincingly demonstrated with the TEM 
(Fig. 5). 
Spider silk, especially the extremely fine threads of cribellate silk 
(Fig. 6), has been studied with the TEM before (Lehmensick and 
Kullman, 1957; Friedrich and Langer, 1969). It should be empha- 
sized here that shadowing with copper yields much more stable prep- 
arations. Ecribellate silk is often too thick (1-2 /x) to be examined 
with the TEM, but accurate measurements of the diameter of various 
threads can be performed (Fig. 7). The substructure of the sticky 
"* Manuscript received by the editor December 10, 1974. 
507 
