Home Improvement Digging Burrowing and Building

Among the social insects, termites are noted for the diversity and complexity of their nest architecture. Both fecal deposits and exogenous materials (soil, wood) transported by the mandibles are used as construction material, and the structure is made cohesive with a mortar of saliva and fecal fluid. Intricate systems of temperature regulation and ventilation are typically incorporated, resulting in a protected, climate-controlled environment for these vulnerable insects (Noirot and Darlington, 2000). Cockroaches exhibit rudimentary forms of these complex construction behaviors, providing support for the notion that termite construction skills are derivations of abilities already present in their blattarian ancestors (Rau, 1941,1943).

A number of cockroach species tunnel in soil, leaf litter, guano, debris, rotten, and sometimes sound, wood (Chapters 2 and 3). Cockroaches also possess the morphological and behavioral requisites for more subtle excavation of substrates, as evidenced in oviparous cockroaches during the deposition and concealment of oothecae (Fig. 7.2) (McKittrick et al. 1961; McKittrick, 1964). On particulate substrates such as sand female Blat-tidae use a raking headstroke to dig a hole, but they gnaw crevices in more solid substances like wood. Blattellidae bite out mouthfuls of material on all substrate types. Legs may be used to help dig holes and to move debris away from the work site. Euzosteria sordida digs a hole using backstrokes of the head, followed by movement of each leg in turn to move sand away from the excavation site (Mackerras, 1965b). After the hole is the appropriate depth, the female has a "molding phase," during which she lines the bottom of the hole with a sticky layer of substrate particles mixed with saliva. The ootheca is then de-

posited in or near the hole, and adjusted into position with the mouthparts. A mixture of saliva and finely masticated substrate is applied to the surface of the egg case, and the remaining gaps are filled with dry material. The whole operation can last more than an hour (McKittrick et al. 1961; McKittrick, 1964). Females can be quite selective in their choice of building material. Rau (1943) noted that Blatta orientalis chooses large grains of sand and discards the small ones. In P. americana the egg case may be plastered with cockroach excrement dissolved in saliva (Rau, 1943). It should be noted in this regard that, like termites, cockroaches produce a heterogeneous mix of excretory products (Nalepa et al., 2001a). These may be distinguished in some species by the behavior of the excretor, the reaction of conspecifics in the vicinity, and the nature of the fecal material. Cockroaches that are domestic pests are well known for producing both solid fecal pellets and smears attached to the substrate. Both Lawson (1965) and Deleporte (1988) describe distinct and systematic defecation behaviors in P. americana that are reminiscent of termites during nest building. These include backing up prior to defecation, then dragging the tip of the abdomen on the substrate while depositing a fecal droplet.

Some cockroach species actively modify their living environment. Arenivaga apacha dwell in the burrows of kangaroo rats, within which they construct small living spaces lined with the nest material of their host (Chapter 3). The soil associated with these spaces is of unusually fine texture because the cockroaches work the soil with their mouthparts, reducing gravel-sized lumps to fine sand and silt-textured soil (Cohen and Cohen, 1976). Eu-blaberus posticus shapes the soft mass of malleable bat guano along the base of cave walls into irregular horizontal galleries (Fig. 9.3). These are subsequently consolidated by calcium carbonate from seepage water (Darlington, 1970). It is unclear whether the cockroaches actively build these structures or whether the hollows are epiphenomena, by-products of the insects' tendency to push themselves under edges and into small irregularities (Darlington, pers. comm. to CAN). The observation by Deleporte (1985) that various developmental stages of P americana dig resting sites in clay walls suggests the former.

Cockroaches in the Cryptocercidae in many ways exhibit nest construction and maintenance behavior comparable to that of dampwood termites (Termopsidae). When initiating a nest, adult Cryptocercus actively excavate galleries; their tunnels are not merely the side effects of feeding activities. They eject frass from the nest, plug holes and gaps (Fig 9.4A), build pillars and walls to partition galleries, and erect barriers when their galleries approach those of families adjacent in the log (Nalepa, 1984,

Fig. 9.3 Shelters fashioned from wet guano along the base of cave walls by Eublaberus posticus, Tamana main cave, Trinidad; note cockroaches in crevices. The insects may actively construct these structures, or they may result from the cockroach tendency to wedge into crevices. From Darlington (1970); photo and information courtesy of J.P.E.C. Darlington.

Fig. 9.3 Shelters fashioned from wet guano along the base of cave walls by Eublaberus posticus, Tamana main cave, Trinidad; note cockroaches in crevices. The insects may actively construct these structures, or they may result from the cockroach tendency to wedge into crevices. From Darlington (1970); photo and information courtesy of J.P.E.C. Darlington.

Fig. 9.4 Constructions of Cryptocercus punctulatus. (A) Detail of material used to plug holes and seal gaps; here it was sealing the interface between a gallery opening and the loose bark that covered it. Both fecal pellets (arrow) and small slivers of wood are present. (B) Sanitary behavior: fecal paste walling off the body of a dead adult (arrow) in a side chamber. An adult male was the only live insect present in the gallery system. Photos by C. A. Nalepa.

Fig. 9.4 Constructions of Cryptocercus punctulatus. (A) Detail of material used to plug holes and seal gaps; here it was sealing the interface between a gallery opening and the loose bark that covered it. Both fecal pellets (arrow) and small slivers of wood are present. (B) Sanitary behavior: fecal paste walling off the body of a dead adult (arrow) in a side chamber. An adult male was the only live insect present in the gallery system. Photos by C. A. Nalepa.

unpubl. obs.). Building activity is most common when the cockroaches nest in soft, well-rotted logs, and, like Zootermopsis and some other termites (Wood, 1976; Noirot and Darlington, 2000), excrement and masticated wood are the principal construction materials. If logs are damp, fecal pellets lose their discrete packaging and become a mass of mud-like frass.

Cryptocercus also exhibits a number of termite-like behaviors in maintaining a clean house. In addition to expelling frass from galleries, adults keep the nursery area (i.e., portion of the gallery with embedded oothecae) clear of fungal growth and the fecal mud that commonly lines the walls of galleries in the remainder of the nest (Nalepa, 1988a). They are known to eat dead nestmates, but, like termites (Weesner, 1953; Dhanarajan, 1978), Cryptocercus will bury unpalatable corpses in unused portions of the gallery (Fig. 9.4B).

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