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

Fig. 3.8 Periplaneta sp. in a sewer manhole in Houma, Louisiana.
From Gary (1950).
with each supporting a different community (Juberthie,
2000b). The twilight zone near the entrance is closest to
epigean conditions and has the largest and most diverse
fauna. Next is a zone of complete darkness with variable
temperature, and finally in the deep interior a zone of
complete darkness, stable temperature, and stagnant air,
where the obligate, troglomorphic fauna appear (Poulson
and White, 1969). The degree of fidelity to a zone varies.
While the Australian Para. rufa is found only from the entrance
to 0.4 km into a cave, Trog. nullarborensis is found
from the entrance to 4.8 km deep; it roams throughout
the cave system and is one of the few troglomorphs
recorded from the twilight zone (Richards, 1971). Eublaberus
posticus and Eub. distanti may segregate in caves
according to their particular moisture requirements. The
former prefers the moist inner sections of caves, while the
latter is more common in drier guano (Darlington, 1970).
The habitable areas of caves, and consequently, populations
of cave organisms, are dynamic—they move, expand,
and contract, depending on climate and on pulses
of organic matter (Humphreys, 1993). After an exceptionally
cool night in Nasty Cave in Australia, for example,
a common Nocticola cockroach could not be found
and was thought to have retreated into cracks during the
unfavorable conditions (Howarth, 1988). Initially a small
species in the subfamily Anaplectinae was sporadically
seen in a Trinidadian cave, subsequently formed a thriving
colony, then was wiped out when the cave flooded. It
did not reappear (Darlington, 1970).
Caves with a source of vertebrate guano support very
different cockroach communities than caves that lack
such input. Guano caves typically contain very large
numbers of few cockroach species able to maintain dense
populations and exploit the abundant, rich, but rather
monotonous food bonanza (Darlington, 1970). Examples
include a population of more than 80,000 Gyna sp.
in a South African cave (Braack, 1989), more than 43,000
Eub. distanti in just one chamber of a cave in Trinidad
(Darlington, 1970) (Fig. 3.9), and Pycnoscelus striatus
found at approximately 2000–3000/m 2 in the Batu Caves
of Malaysia (McClure, 1965). A similar scenario is that of
approximately 3000 P. americana /m 2 in a sewer system
more than 27 m beneath the University of Minnesota
campus (Roth and Willis, 1957). In guano caves, the distribution
of cockroaches usually coincides with that of
bats and their excrement (Braack, 1989). Some species are
consistently associated with bat guano, wherever it is
found. One South African Gyna sp. was present in all batinhabited
caves and cave-like habitats, including the roof
of a post office (Braack, 1989).
Highly troglomorphic cockroach species generally
support themselves on less rich, less abundant food
sources. Trogloblattella chapmani is typically found remote
from guano beds in passages floored by damp sticky
clay or silt (Roth, 1980). Metanocticola christmasensis is
associated with the often luxuriant tree root systems that
penetrate caves (Roth, 1999b), but their diet is unknown
(Roth, 1999b). Troglomorphic cockroaches tend to move
Fig 3.9 Habitat stratification in Eublaberus distanti in Guanapo
Cave, Trinidad. (A) Adults on walls of cave; (B) nymphs
on surface of fruit bat guano. Photos courtesy of J.P.E.C. Darlington.
HABITATS 53