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E. B. EDNEY
glyphicus, not only lives longer in dry air, but tolerates a greater degree
of dehydration than does the more mesic grasshopper, Anacridium melanorhodon. The former withstood dehydration for 18 days and lost 35% of
its original weight, while the latter died after losing 26% in 11 days
(Abushama, 1968, 1970). But this is an isolated instance, and there is,
in fact, insufficient evidence to say whether or not desert species are able
to tolerate greater water loss or lower water contents than others. However,
the known tolerances are much greater than that of man, where a loss
of 10-12% renders subsequent recovery doubtful, and at least equal to
that of the renowned camel (Schmidt-Nielsen, 1964). But the reason why
some arthropods survive in dry conditions longer than others is much more
likely to be found in their greater efficiency with respect to water
conservation.
Turning now to temperature tolerances, we find an almost equally unsatisfactory situation; not on account of a lack of statements about lethal
temperatures, but because the information has been obtained in so many
different ways as to make comparisons almost pointless. Duration of exposure obviously affects the lethal level, so does the rate at which the rise
in temperature is imposed. Humidity affects the lethal temperature (although probably only if this is measured as an ambient temperature), so
does previous acclimation (for a review of these matters, see Bursell,
1964b, 1970).
It may very well be true that by and large arthropods subject to high
temperatures in their natural habitats have higher lethal temperatures than
others. Examples can be chosen to illustrate this point—thus the mole
cricket, Gryllotalpa, is normally active between —2.5° and - f l l . 5 ° C and
is killed if the temperature is raised to 20.5°C, while the firebrat, Thermobia, a favorite habitat of which is bakers' hobs, is active between 12°
and 50°C and dies at 51.3°C (Edwards and Nutting, 1950). It would
be rash to say, however, that the relationship has been generally established. In most insects the upper limit lies somewhere between 40° and
50°C. Cloudsley-Thompson (1962a) found some desert arthropods to
have the following lethal temperatures for 24 hours exposures at 10% relative humidity: the scorpion, Leiurus, at 47°C; the camel spider,
Galeodes at 50°C; and the beetles, Pimelia grandis and Ocnera hispida,
at 43° and 45°C, respectively. Hafez and Makky (1959) found the
tenebriond beetle, Adesmia, to be able to withstand slowly rising soil temperatures up to 53°C, and Berry and Cloudsley-Thompson (1960) recorded the presence of one grasshopper while the surface temperature in
the Red Sea Hills was 83.5°C, (but we do not know the temperature of
the insects themselves). The desert beetle, Centrioptera muricata, lives for
nearly 30 minutes at 50°C in nearly dry air (Ahearn, 1970a).
E. B. EDNEY
glyphicus, not only lives longer in dry air, but tolerates a greater degree
of dehydration than does the more mesic grasshopper, Anacridium melanorhodon. The former withstood dehydration for 18 days and lost 35% of
its original weight, while the latter died after losing 26% in 11 days
(Abushama, 1968, 1970). But this is an isolated instance, and there is,
in fact, insufficient evidence to say whether or not desert species are able
to tolerate greater water loss or lower water contents than others. However,
the known tolerances are much greater than that of man, where a loss
of 10-12% renders subsequent recovery doubtful, and at least equal to
that of the renowned camel (Schmidt-Nielsen, 1964). But the reason why
some arthropods survive in dry conditions longer than others is much more
likely to be found in their greater efficiency with respect to water
conservation.
Turning now to temperature tolerances, we find an almost equally unsatisfactory situation; not on account of a lack of statements about lethal
temperatures, but because the information has been obtained in so many
different ways as to make comparisons almost pointless. Duration of exposure obviously affects the lethal level, so does the rate at which the rise
in temperature is imposed. Humidity affects the lethal temperature (although probably only if this is measured as an ambient temperature), so
does previous acclimation (for a review of these matters, see Bursell,
1964b, 1970).
It may very well be true that by and large arthropods subject to high
temperatures in their natural habitats have higher lethal temperatures than
others. Examples can be chosen to illustrate this point—thus the mole
cricket, Gryllotalpa, is normally active between —2.5° and - f l l . 5 ° C and
is killed if the temperature is raised to 20.5°C, while the firebrat, Thermobia, a favorite habitat of which is bakers' hobs, is active between 12°
and 50°C and dies at 51.3°C (Edwards and Nutting, 1950). It would
be rash to say, however, that the relationship has been generally established. In most insects the upper limit lies somewhere between 40° and
50°C. Cloudsley-Thompson (1962a) found some desert arthropods to
have the following lethal temperatures for 24 hours exposures at 10% relative humidity: the scorpion, Leiurus, at 47°C; the camel spider,
Galeodes at 50°C; and the beetles, Pimelia grandis and Ocnera hispida,
at 43° and 45°C, respectively. Hafez and Makky (1959) found the
tenebriond beetle, Adesmia, to be able to withstand slowly rising soil temperatures up to 53°C, and Berry and Cloudsley-Thompson (1960) recorded the presence of one grasshopper while the surface temperature in
the Red Sea Hills was 83.5°C, (but we do not know the temperature of
the insects themselves). The desert beetle, Centrioptera muricata, lives for
nearly 30 minutes at 50°C in nearly dry air (Ahearn, 1970a).