CORRELATION BETWEEN SEGMENT LENGTH AND 
SPINE COUNTS IN TWO SPIDER SPECIES OF 
ARANEUS (ARANEAE: ARANEIDAE)* 
By L. David Carmichael 
Museum of Comparative Zoology 
Abstract 
Observations made on several hundred adult male spiders of 
two species of Araneus indicate a highly significant correlation 
(p<0.ooi) between the length of a segment (tibia of the second 
leg) and the number of macrosetae (“spines”) present on the seg- 
ment. This result is further supported by observations on the first 
tibiae of about twenty male A. trifolium, one of the two species, and 
by a few observations on immatures of the two species. A short 
summary of the methods used in taking the measurements and mak- 
ing the calculations is followed by discussion of the implications of 
this correlation with reference to species determination and geo- 
graphic variation. 
Methods 
The study was done on two species of common North American 
spiders, Araneus trifolium (Hentz) and A . marmoreus Clerck. 185 
male specimens of A. trifolium yielded 347 tibiae of the second leg 
(some specimens had lost one leg) ; the length of this segment was 
measured, and the number of spines on the segment was counted. 
In addition, lengths and spine counts were taken for the first tibiae 
of 23 of the spiders, yielding 41 observations. Similarly, 120 speci- 
mens of A. marmoreus yielded 210 second tibiae; the length was 
measured, and two spine counts were made: the total number on 
the tibia, and the number of modified, “dentiform” 1 spines (see 
Figure 3). The samples of both species were museum collections, 
and represented almost the entire known range of each in North 
America, extending from coast to coast and roughly from the 35th 
to the 55th parallels. 
The spines of the second tibia, like all the spines of these spiders, 
are actually setae in the entomological sense ; they are set in a socket 
* Manuscript received by the editor January 10, 1973 
Term used by Locket & Millidge (1953), pp. 120, 121. 
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