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

Fig. 10.1 Decomposition of logs by Cryptocercus punctulatus,
Mountain Lake Biological Station, Virginia. (A) Frass pile outside
gallery entrance. (B) Small log hollowed and filled entirely
with frass and fecal pellets. Photos by C.A. Nalepa.
pushed to the outside of the logs, no doubt influencing
local populations of bacteria, fungi, and microfauna (Fig.
10.1). The typically substantial body size of these insects
contributes to their impact; some species of Panesthia exceed
5 cm in length (Roth, 1979c). Although these two
taxa are the best known, many cockroach species potentially
influence log decomposition (Table 3.2).
Xeric Habitats
Cockroaches are known to participate in the breakdown
of plant organic matter in deserts and other arid and
semiarid landscapes, and have a direct and substantial
impact on nutrient flow. Anisogamia tamerlana is the
main consumer of plant litter in Turkmenistan deserts
(Kaplin, 1995), and cockroaches in the genus Heterogamia
are the most abundant detritivore in the Mediterranean
coastal desert of Egypt. The latter dominate the
arthropod fauna living beneath the canopy of desert
shrubs, with up to 116,000 cockroaches/ha, comprising
82% of the arthropod biomass (Ghabbour et al., 1977;
Ghabbour and Shakir, 1980). The daily food consumption
of An. tamerlana is 17–18% of their dry body mass,
with 57–69% assimilation. Females and juveniles consume
840–1008 g/ha dry plant debris and produce 259–
320 g/ha of excrement (Kaplin, 1995). These cockroaches
improve the status of desert soils via their abundant fecal
pellets, the nitrogen content of which is 10 times that of
their leaf litter food source (El-Ayouty et al., 1978).
Many of the ground-dwelling, wingless cockroaches of
Australia are important in leaf litter breakdown. This is
particularly true in stands of Eucalyptus, where litter production
is high relative to other forest types, leaves decompose
slowly, and more typical decomposers such as
earthworms, isopods, and millipedes are uncommon
(Matthews, 1976). The beautiful Striped Desert Cockroach
Desmozosteria cincta, for example, lives among
twigs and branches at the base of eucalypts (Rentz, 1996).
In hummock grasslands and spinifex, genera such as
Anamesia feed on the dead vegetation trapped between
the densely packed stems (Park, 1990). The litter-feeding,
soil-burrowing Geoscapheini are associated with a variety
of Australian vegetation types ranging from dry sclerophyll
to rainforest, and have perhaps the most potential
ecological impact. First, they drag quantities of leaves,
twigs, grass, and berries down into their burrows, thus
moving surface litter to lower soil horizons. Second, they
deposit excreta deep within the earth. Fecal pellets are
abundant and large; those of Macropanesthia rhinoceros
are roughly the size and shape of watermelon seeds.
Third, burrowing by large-bodied insects such as these
has profound physical and chemical effects on the soil.
Burrows influence drainage and aeration, alter texture,
structure, and porosity, mix soil horizons, and modify
soil chemical profiles (Anderson, 1983; Wolters and
Ekschmitt, 1997). The permanent underground lairs of
M. rhinoceros have plastered walls and meander just beneath
the soil surface before descending in a broad spiral
(Fig. 10.2). The deepest burrows can be 6 m long, reach 1
m below the surface, and have a cross section of 4–15 cm.
Burrows may be locally concentrated; the maximum density
found was two burrows/m 2 , with an average of 0.33/
m 2 (Matsumoto, 1992; Rugg and Rose, 1991).
Cockroaches in arid landscapes nicely illustrate two
subtleties of the ecological role of decomposers: first, an
often mutualistic relationship with individual plants, and
second, the key role of gut microbiota. In sparsely vegetated
xeric habitats, the density of cockroaches generally
varies as a function of plant distribution. In deserts,
Polyphagidae are frequently concentrated under shrubs
(Ghabbour et al., 1977), and the burrows of Australian
Geoscapheini are often associated with trees. Macropanesthia
heppleorum tunnels amid roots in Callitris-
Eucalyptus forest, and Geoscapheus woodwardi burrows
are located under overhanging branches of Acacia spp. in
mixed open forest (Roach and Rentz, 1998). Not only are
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