VI. DESERT ARTHROPODS
349
Desert sand roaches, Arenivaga investigata, have an upper lethal temperature of about 48.5°C in dry air and about 46.5°C in moist air (for
30 minutes exposures), unless they have been acclimated to lower temperatures, when the figures are 47.5° and 45.5°C, respectively (E. B.
Edney, unpublished). These figures are slightly higher than those for the
domestic cockroach, Periplaneta americana. At the lower end of the range,
cold-acclimated arenivage can withstand 1°C for 5 minutes, while warmacclimated ones go into a cold coma even at 4°C. Once again Periplaneta
is rather less hardy, so that it looks as if Arenivaga has both a higher
and a lower temperature tolerance than Periplaneta.
I have recently measured the upper lethal temperatures of some
tenebrionid beetles that live in the Namib Desert of southwest Africa and
of others that live in the moister surroundings of the Eastern Cape
Province (Edney, 1971b). The highest temperature tolerable for 30 minutes in saturated air was 51°C for Onymacris plana, a large beetle of the
sand dunes which is active by day. Other species, such as O. rugatipennis
and O. laeviceps, which seek cover earlier in the forenoon and emerge
later in the afternoon, were not quite so hardy, surviving at 49°-50°C,
while the more mesic species, Trigonopus capicola and another Trigonopus
species, died at 45°C.
There has been some useful recent work on the determination of body
temperatures in the field, and this is discussed in Section V. Here we note
the general point that even for small animals, body temperature may be
significantly different from either air or soil temperature in the vicinity,
and a better understanding of the heat relationships of desert arthropods
will be achieved only when we know a good deal more about actual body
temperatures in relation to desert conditions.
A few examples of extremely high temperature tolerances during cryptobiosis have been established. Larvae of the chironomid midge, Polypedilum
vanderplanki, live in rock pools which periodically dry up. The larvae then
suffer almost complete dehydration, and in this condition can withstand
102°C for 1 minute or so, after which, upon rehydration, they pupate successfully (Hinton, 1960). This is certainly an outstanding example of
adaptation to a desert environment, even though the animal can hardly
be said to be alive at the time of maximum stress.
V. Body Temperature in the Field
A. GENERAL CONSIDERATIONS
The manner in which body temperature is determined by environmental
factors is very complex. The factors involved, including solar radiation
349
Desert sand roaches, Arenivaga investigata, have an upper lethal temperature of about 48.5°C in dry air and about 46.5°C in moist air (for
30 minutes exposures), unless they have been acclimated to lower temperatures, when the figures are 47.5° and 45.5°C, respectively (E. B.
Edney, unpublished). These figures are slightly higher than those for the
domestic cockroach, Periplaneta americana. At the lower end of the range,
cold-acclimated arenivage can withstand 1°C for 5 minutes, while warmacclimated ones go into a cold coma even at 4°C. Once again Periplaneta
is rather less hardy, so that it looks as if Arenivaga has both a higher
and a lower temperature tolerance than Periplaneta.
I have recently measured the upper lethal temperatures of some
tenebrionid beetles that live in the Namib Desert of southwest Africa and
of others that live in the moister surroundings of the Eastern Cape
Province (Edney, 1971b). The highest temperature tolerable for 30 minutes in saturated air was 51°C for Onymacris plana, a large beetle of the
sand dunes which is active by day. Other species, such as O. rugatipennis
and O. laeviceps, which seek cover earlier in the forenoon and emerge
later in the afternoon, were not quite so hardy, surviving at 49°-50°C,
while the more mesic species, Trigonopus capicola and another Trigonopus
species, died at 45°C.
There has been some useful recent work on the determination of body
temperatures in the field, and this is discussed in Section V. Here we note
the general point that even for small animals, body temperature may be
significantly different from either air or soil temperature in the vicinity,
and a better understanding of the heat relationships of desert arthropods
will be achieved only when we know a good deal more about actual body
temperatures in relation to desert conditions.
A few examples of extremely high temperature tolerances during cryptobiosis have been established. Larvae of the chironomid midge, Polypedilum
vanderplanki, live in rock pools which periodically dry up. The larvae then
suffer almost complete dehydration, and in this condition can withstand
102°C for 1 minute or so, after which, upon rehydration, they pupate successfully (Hinton, 1960). This is certainly an outstanding example of
adaptation to a desert environment, even though the animal can hardly
be said to be alive at the time of maximum stress.
V. Body Temperature in the Field
A. GENERAL CONSIDERATIONS
The manner in which body temperature is determined by environmental
factors is very complex. The factors involved, including solar radiation