Journal of Cave and Karst Studies - ISSN 1090-6924
Volume 64 Number 2: 126-131 - August 2002

A publication of the National Speleological Society

Leg Attenuation and Seasonal Femur Length: Mass Relationships in Cavernicolous Crickets (Orthoptera: Gryllidae and Rhaphidophoridae)
Eugene H. Studier, Kathleen H. Lavoie and Francis G. Howarth

Abstract

We report here some factors that affect the relationship between hind femur length (HFL) to crop-empty live weight (CELW) and propose a quantitative, non-lethal measurement ratio that has potential as an index of extent of adaptation to a cavernicolous existence in “crickets”. Curvilinear relationships exist between HFL and CELW for camel crickets (Ceuthophilus stygius) and cave crickets (Hadenoecus subterraneus). The relationships differ significantly between the species and also by gender within both species and, in cave crickets, by season as well. In C. stygius, females of small HFL are slightly lighter, and those of large HFL slightly heavier than males. In H. subterraneus, females have progressively greater CELW than males as HFL increases. In adult H. subterraneus of identical HFLs, CELW is greatest in fall and least in spring, i.e., individuals are most robust in the Fall in these long-lived crickets, probably due to seasonal constraints on surface feeding. An attenuation index of CELW/HFL³ yields a ratio that ranks the extent of adaptation to cave life in these two and eight other species of variously adapted cavernicolous and epigean “crickets”. Lower values of the attenuation index indicate greater adaptation to cavernicolous existence. The three gryllid species from Hawaii Island are closely related and include the blind, obligate cave cricket, Caconemobius varius, and two surface species, the lava flow cricket, Caconemobius fori, and the marine littoral cricket, Caconemobius sandwichensis. The latter two species are nocturnal scavengers on barren rock habitats. The lower CELW/HFL³ ratio in lava flow crickets suggest they use caves more frequently for daytime roosts than does the marine littoral species.

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