Seasonal aspects of the life cycle of solifuges (Arachnida, Solifugae) as compared with pseudoscorpions (Arachnida, Pseudoscorpiones)

Solifuges (order Solifugae) and pseudoscorpions (order Pseudoscorpiones) united into the superorder Haplocnemata (Shultz, 2007) are nevertheless characterized by essential differences both in morphological and biological characters. Analysis of available information on the biology and life cycles of these arachnids revealed a clear difference between the daily rhythms of activity: their presence in solifuges and their absence in pseudoscorpions. However, this concerning the seasonal adaptations in the two orders is not simple since they demonstrate not only differences but also a lot of similarities. All the studied solifuges are characterized by the seasonally timed stenochronous (heterodynamic) type of development which is characteristic of species with uni-, bi-, and semi-voltine development (i.e., to life cycles completed within a year, half a year, and several years), as well as to species combining different forms of voltinism. This type of development is not only prevalent in solifuges (as in pseudoscorpions and other arachnids) but appears to be the only one, since no cases of eurychronous (homodynamic) development have been found in solifuges; whereas pseudoscorpions and other arachnids develop both steno- and eurychronously. The initial ontogenetic stages remain in underground shelters (brood burrows in solifuges and brood chambers in pseudoscorpions). The first nymphal stages (I instar nymphs in solifuges, protonymphs in pseudoscorpions) are embryonized; active life outside the brood burrows starts with II instar nymphs in solifuges and with deutonymphs in pseudoscorpions.