340
E. B. EDNEY
collembolans may again be involved, although the normal cuticle of the
cockroach seems to be very efficient at water absorption even against steep
osmotic gradients (Beament, 1965). However, there is no suggestion that
desert arthropods are particularly adept in this respect.
J. ABSORPTION OF WATER VAPOR
An interesting phenomenon which may be of great adaptive value for
desert arthropods is the ability to absorb water vapor from unsaturated
air. This process, the mechanism of which is still incompletely understood,
is known to occur in a number of arachnids including both ixodid and
argassid ticks (Browning, 1954; Lees, 1946) and mites (Kanungo, 1965;
Knülle and Wharton, 1964; Solomon, 1966; Wharton and Devine, 1968).
It has also been found in insects, including the mealworm Tenebrio molitor
(Mellanby, 1932a), fleas (Edney, 1947; Knülle, 1967), firebrats (Thermobia) (Beament et al, 1964; Noble-Nesbitt, 1969), the related thysanuram Ctenolepisma (Heeg, 1967; Edney, 1971a) and the psocid
Liposcelis (Knülle and Spadafora, 1969). In most cases the limiting humidity lies between 80 and 90%, but it may be as low as 50% in fleas
and firebrats and 58% in psocids. More complete lists are given by
Noble-Nesbitt (1969) and by Berridge (1970) who included equilibrium
humidities.
The habitat of most of these arthropods is on the whole xeric, with little
free water available, so that the process could be a useful one. It is therefore interesting to find a further insectan example from the sand dunes
of a typical desert. The insect is a species of polyphagid cockroach,
Arenivaga investigata (Friauf and Edney, 1969). It has never been found
apart from sand dunes, where it seems to be associated with such plants
as the creosote bush (Larrea divaricata) a salt bush (Atriplex canescens)
and Dalea fremonti. The adult females are neotenic and wingless (Fig.
12), while the adult males are fully winged and look much like an ordinary
cockroach. Very little is known about their natural history, although some
aspects of their behavior have been reported by Edney et al. (1973).
Males, females, and nymphs all live below the surface of sand, although
the alate males often emerge and may be taken at lights by night. Nymphs
and females wander about just below the surface at night leaving telltale
ridges on the sand as they go. Occasionally a female may emerge above
the surface, and Fig. 12b shows evidence of this in the form of her tracks.
These insects feed on a variety of plant and animal remains which are
fairly abundant in the dunes—we have never found them feeding on living
plants. Scorpions have been seen feeding on them. Temperatures and humidities in the habitat of these sand roaches have now been adequately
E. B. EDNEY
collembolans may again be involved, although the normal cuticle of the
cockroach seems to be very efficient at water absorption even against steep
osmotic gradients (Beament, 1965). However, there is no suggestion that
desert arthropods are particularly adept in this respect.
J. ABSORPTION OF WATER VAPOR
An interesting phenomenon which may be of great adaptive value for
desert arthropods is the ability to absorb water vapor from unsaturated
air. This process, the mechanism of which is still incompletely understood,
is known to occur in a number of arachnids including both ixodid and
argassid ticks (Browning, 1954; Lees, 1946) and mites (Kanungo, 1965;
Knülle and Wharton, 1964; Solomon, 1966; Wharton and Devine, 1968).
It has also been found in insects, including the mealworm Tenebrio molitor
(Mellanby, 1932a), fleas (Edney, 1947; Knülle, 1967), firebrats (Thermobia) (Beament et al, 1964; Noble-Nesbitt, 1969), the related thysanuram Ctenolepisma (Heeg, 1967; Edney, 1971a) and the psocid
Liposcelis (Knülle and Spadafora, 1969). In most cases the limiting humidity lies between 80 and 90%, but it may be as low as 50% in fleas
and firebrats and 58% in psocids. More complete lists are given by
Noble-Nesbitt (1969) and by Berridge (1970) who included equilibrium
humidities.
The habitat of most of these arthropods is on the whole xeric, with little
free water available, so that the process could be a useful one. It is therefore interesting to find a further insectan example from the sand dunes
of a typical desert. The insect is a species of polyphagid cockroach,
Arenivaga investigata (Friauf and Edney, 1969). It has never been found
apart from sand dunes, where it seems to be associated with such plants
as the creosote bush (Larrea divaricata) a salt bush (Atriplex canescens)
and Dalea fremonti. The adult females are neotenic and wingless (Fig.
12), while the adult males are fully winged and look much like an ordinary
cockroach. Very little is known about their natural history, although some
aspects of their behavior have been reported by Edney et al. (1973).
Males, females, and nymphs all live below the surface of sand, although
the alate males often emerge and may be taken at lights by night. Nymphs
and females wander about just below the surface at night leaving telltale
ridges on the sand as they go. Occasionally a female may emerge above
the surface, and Fig. 12b shows evidence of this in the form of her tracks.
These insects feed on a variety of plant and animal remains which are
fairly abundant in the dunes—we have never found them feeding on living
plants. Scorpions have been seen feeding on them. Temperatures and humidities in the habitat of these sand roaches have now been adequately