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

these could range from a few millimeters in size to the
largest caverns, and may occur in soil layers, fractured
rock, lava tubes, and talus slopes (Howarth, 1983). All of
these spaces, whether created by the insect or naturally
occurring in soil, leaf litter, guano, debris, rotten wood, or
rock are similar in that they are dark, often humid, and
buffered from temperature fluctuations.
It is obvious that a crevice-seeking/burrowing lifestyle
is suited to a wide range of habitats, as long as dark, humid
spaces are present or the substrate allows for their
creation. Burrowing, the act of manufacturing or enlarging
a space for shelter, is common among Blattaria, but
there is a fine line of distinction between a cockroach
forcing itself into an existing void, such as one under
loose bark, and actually tunneling into the soft, rotted
wood beneath. Both photonegativity and positive thigmotaxis
predispose cockroaches to burrowing behavior.
Beebe (1925, p. 147) offers a vivid definition of positive
thigmotaxis: “having the irresistible desire to touch or be
touched by something, above, below, and—a thigmotac’s
greatest joy—on all sides at once” (Fig. 3.7). Additional
traits that favor successful colonization of dark, dank
habitats include the use of non-visual cues in detecting
food, mates, and predators, a lack of highly specialized
feeding habits, and physiological adaptations to food
scarcity (Darlington, 1970; Culver, 1982; Langecker,
2000).
A subterranean niche offers a relatively simple habitat,
with climatic stability and a degree of protection from
predators. These benefits are countered by physical and
physiological challenges that must be met for successful
occupancy. Costs may be incurred in obtaining or constructing
burrows and shelters. The insect must cope with
an environment that is aphotic, low in production, and
high in humidity, endo- and ectoparasites, and pathogens
(Nevo, 1999). Suboptimum O 2
and toxic CO 2
levels are
also common in burrows, in caves, in wet, decaying logs,
at high altitudes, and when insects are encased in snow
and ice (Mani, 1968; Cohen and Cohen, 1981; Hoback
and Stanley, 2001).
For our discussion of cockroach habitats, we recognize
five broad subdivisions: (1) cockroaches that shelter in
Fig. 3.7 Section through a crevice showing the characteristic
rest position of a cockroach. From Cornwell (1968), with permission
of Rentokil Initial plc.
loose substrates (plant litter, guano, uncompacted soil,
dust); (2) crevice fauna (under logs, bark, stones, and
clumps of earth, in rolled leaves, leaf bases, bark crevices,
scree); (3) those that excavate burrows in a solid substrate
(wood, soil); (4) those that make use of existing nests or
burrows (active or abandoned nests of social insects and
small vertebrates); and (5) those in large burrows: caves
and cave-like habitats like sewers and mines. We then address
cockroaches found in three rather specialized habitats:
deserts, aquatic environments, and the forest canopy.
We are aware that there are difficulties in adhering to
these distinctions, as the subdivisions grade into each
other and species often span categories. Many cockroaches
that do not routinely inhabit a burrow, for example,
may construct underground chambers for rearing the
young, for hibernation, for aestivation, or for molting.
Many species travel between shelter and sites of feeding
and reproductive activity; others (especially those in categories
3 and 4) live their entire life in shelter, except for
brief dispersal periods. Some cockroaches never leave
sheltered spaces (some cases of category 5). Those in category
3 actively create their living space, while those in the
other four categories generally choose advantageous locations
among existing alternatives. In each category,
variation exists that is rooted in resource quality, quantity,
and location.
In Loose Substrate
Cockroaches in this category either tunnel in uncompacted
substrate (loose soil, dust, sand, guano), which
may collapse around them as they travel through it, or
they utilize small, preexisting spaces (dirt clods, leaf litter,
and other plant debris), which their activities may enlarge.
Many remain beneath the surface only during inactive
periods, although those in guano and leaf litter,
particularly juveniles, may conduct all activities there.
Certainly the largest class in this category are cockroaches
that tunnel in plant litter found on forest floors, in the
suspended soils of the canopy (e.g., in epiphytes, treeholes,
tree forks), and in piles concentrated by the actions
of wind, water, or humans. Some species tunnel only as a
defense from predators, or in response to local or seasonal
conditions. Substrate categories are often fluid. Those
that burrow in guano may also burrow in dirt, and those
that tunnel in leaf litter may continue into the superficial
layers of soil. Adults of Therea petiveriana in the dry,
scrub jungles of India burrow in soil, leaf litter, and debris
(including garbage dumps) during their non-active
period (Livingstone and Ramani, 1978). The nymphs are
subterranean and prefer the zone between the litter and
the underlying humus, but may descend 30 cm during
dry periods (Bhoopathy, 1997). Other versatile burrowers
HABITATS 45