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Abstract.  The larvae of the antlion Euroleon nostras are pit‐builders, constructing pitfall traps in loose sand. The number of pits and the pit diameter are recorded when larvae are kept in substrates with different particle sizes. The most convenient pit‐building sand fractions are two fractions with fine sand (≤ 0.23 mm; 0.23–0.54 mm). The largest pits are constructed in sand with a particle size of 0.23–0.54 mm. In this sand fraction, larvae of all three instars most readily build pits. No pits are constructed in sand with a particle size greater than 1.54 mm. First‐ and second‐instar larvae avoid building pits in substrates of particle size 1–1.54 mm, but third‐instar larvae construct pits in this sand fraction. It is assumed that the antlion is capable of distinguishing between substrate types and this hypothesis is tested by giving larvae the choice of building a pit in one of four particle‐size fractions. Larvae of all three instars prefer to build pits in the fraction with a particle size of 0.23–0.54 mm. Only third‐instar larvae build pits in all four fractions, but only occasionally in the coarser fraction.

During the growth period, in surface habitats, spiders catch enough prey to feed normally. In contrast, in the cave entrance zone, prey may be relatively scarce. Meta menardi inhabits this cave section, resulting in temporary starvation. We studied structural changes in the midgut epithelial cells of M. menardi during a short-term and a medium-term controlled starvation to mimic the occasional starvation in caves, during spring and autumn. Digestive cells, secretory cells and adipocytes were examined before the experimental starvation, in the middle and at the end of starvation. We used light microscopy, transmission electron microscopy and specific histochemical methods for the detection of lipids, polysaccharides and proteins. Detection of lysosomes, autolysosomes and apoptosis was also carried out. The general structures of the cells did not change during the experimental starvation in either season, while some specific differences in the ultrastructure were observed. In both sexes, in both seasons, the amounts of lipids, glycogen and proteins decreased during starvation. Larger amounts of lipids were found in autumn, while there were no significant differences in the amounts of glycogen and proteins. In both sexes, in both seasons, autophagy and apoptosis intensified with starvation in progress, but more intensively in females. Thus, autumn individuals, in contrast to spring ones, compile energy-supplying stores to confront the subsequent winter deficiency of prey in caves, while the cellular ultrastructures undergo the same starvation-dependant changes at any time during the growth period.

Terrestrial animals in subterranean habitats are often classified according to their degree of morphological or ecological specialization to the subterranean environment. The commonly held view is that, as distance into a cave increases, the frequency of morphologically specialized, i.e., troglomorphic, species or ecological specialization will increase. We tested this hypothesis for the fauna in 54 caves in Slovenia-the classical land for subterranean biology. We found that there exist two ecologically well separated terrestrial subsurface faunas: one shallow and one deep. 1) The shallow subterranean fauna, adapted to the terrestrial shallow subterranean habitats (SSHs) in the upper 10 m of subsurface strata, is most diverse. It consists of randomly distributed non-troglobionts and a major group of troglobionts adapted to the soil root zone. 2) The deep subterranean fauna is represented by a minor group of troglobionts, adapted to caves. Troglobionts are strictly divided between the two faunas. There is strong evidence that in karstic ecosystems with deep-rooted vegetation this might be a global pattern, or that in these locations only the shallow subterranean fauna exist.

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