Cockroache; Ecology, behavior & history - W.J. Bell

when maintained in laboratory culture (Reuben, 1988),
and nothing is known about the many diurnal Australian
species that enjoy sunbasking. Perhaps as in some birds
(Dean and Williams, 1999) the added heat helps speed digestion
of a cellulose-based diet. Juvenile Phyllodromica
maculata live on the dry, grassy hillsides of Bavaria, prefer
low humidity, and do not aggregate (Gaim and
Seelinger, 1984). Studies of laboratory-bred cockroaches
indicate a variety of methods for dealing with heat and
water stress. Periplaneta americana, B. germanica, and
Blatta orientalis can withstand a body weight loss of 30%
and still recover successfully when given an opportunity
to drink water (Gunn, 1935). Periplaneta fuliginosa and
R. maderae nymphs use the salivary glands as water storage
organs (Laird et al., 1972; Appel and Smith, 2002).
Gromphadorhina brauneri and P. americana maintain
body temperatures below that of surrounding air by
evaporative cooling (Janiszewski and Wysocki, 1986),
and there is some evidence that P. americana can close
dermal gland openings to conserve water (Machin et al.,
1994). The physiology of water regulation in cockroaches
is addressed in detail by Edney (1977), Mullins (1982),
and Hadley (1994).
Aquatic Habitats
Most amphibious and quasi-aquatic cockroaches fall into
two basic groups: those that live in phytotelmata (small
pools of water within or upon plants) and those associated
with rivers, streams, and ponds. In both cases, the insects
live at the surface of the water or on solid substrate
in its immediate vicinity, but submerge to hunt for food
or to escape predators. About 62 species (25 genera) of
cockroaches have been collected from the leaf bases of
bromeliads (Roth and Willis, 1960; Rocha e Silva Albuquerque
and Lopes, 1976), but it is unknown how many
of these are restricted to this habitat. One example is
Dryadoblatta scotti, a large, handsome, Trinidadian cockroach
found in considerable numbers in epiphytic bromeliads;
they rest just above the surface of the water or are
partly immersed in it (Princis and Kevan, 1955). Nymphs
of Litopeltis sp. are encountered during the day at all times
of the year in the erect bracts of Heliconia, which collect
and hold water even during the dry season of Costa Rica.
The cockroaches forage at night on the outer and inner
surfaces of the bracts, feeding on mold and decayed areas
(Seifert and Seifert, 1976).
Numerous species in at least six genera of Epilamprinae
live near streams or pools, usually in association with
rotting vegetation amid rocks along the edge of the water.
Poeciloderrhis cribrosa verticalis in Rio de Janeiro (Rocha
e Silva Albuquerque et al., 1976) and Rhabdoblatta annandalei
in Thailand (LMR, pers. obs.) occur near swiftmoving
streams, and Rhabdoblatta stipata in Liberia occurs
on logs or mats floating directly in the current (Weidner,
1969). The cockroaches submerge in response to disturbance
or when a shadow passes overhead, and swim
rapidly below the surface for a minute or two. They then
cling to submerged vegetation for up to 15 min before
climbing to the surface (e.g., Epilampra maya [reported
as Ep. abdomennigrum] in Panama—Crowell, 1946).
It has been debated as to whether aquatic cockroaches
have morphological adaptations that enable underwater
respiration. In most species observed to date, it appears
that the insects use the abdominal tip as a snorkel, use a
bubble of air as an accessory gill, or both. Weidner (1969)
writes that individuals of Rha. stipata inspire via spiracles
located on conical projections adjacent to the cerci, and
die in 6–12 hr if the abdominal tip is held under water.
Opisthoplatia maculata also has spiracular openings at
the tip of abdominal projections, and these are protected
by long hairs on the ventral surface of the cerci (Takahashi,
1926). Annandale (1906) suggested that the position
of these posterior spiracles is an adaptation to an
aquatic lifestyle; however, Shelford (1907) and Chopard
(1938) point out that this character is present in many
terrestrial cockroach species. Scanning electron micrographs
of Ep. abdomennigrum reveal no unique adaptations
of the terminal spiracles; they appear to be identical
to those elsewhere on the body (WJB, unpubl. obs.).
There are distinct patches of hairs on the ventral side of
the cerci in older nymphs that that are absent in other
Epilampra species examined; however, these hairs are
quite distant from the terminal spiracles. The tracheal
systems of aquatic and terrestrial cockroaches are morphologically
distinct. The tracheae of the latter are
thread-like, silvery in appearance, and dilated to their
maximum with air. The tracheae of amphibious cockroaches
are strap-like, not silvery, and contain just a few
scattered air bubbles. Shelford (1916) suggested that the
differences are rooted in the need for the amphibious
species to be “sinkable,” which would be prevented by internal
accumulated air.
A large bubble is apparent beneath the pronotal shield
of several aquatic species when they are submerged. The
air is trapped by easily wetted, long hairs on the underside
of the thorax (Takahashi, 1926; Crowell, 1946); these
hairs also occur on terrestrial species. Some observers
suggest that the bubble is formed by air taken in through
the terminal abdominal spiracles, which then issues from
the prothoracic spiracles in Ep. maya and O. orientalis
(Shelford, 1907; Takahashi, 1926). Although this may explain
the formation of the thoracic air bubble, air usually
moves posteriorly through the tracheal system of blaberids
(Miller, 1981), and recent observations suggest a
different source of the bubble. WJB (unpubl. obs.) ob-
HABITATS 57