In form and build, though not in proportions and habits, mantids, particularly the small, brown ones that hunt on bark or in leaf litter, recall their cousins the cockroaches, especially when viewed from the side and bathed in a backlight that accentuates their low profile of leathery forewings (tegmina), angled heads and widely splayed legs. But the former arouse an awe that borders on fearful respect, while the latter inspire quite different sentiments, even in those with a soft spot for terrestrial arthropods.
Scampering, scuttling, scrounging and squirreling themselves into dark cracks and forgotten drawers, the roaches of urban domains embody to many all that is nasty and horrid about their kind. In life, the insects incite disgust as they emerge from sewers and refuse bins to fondle our larders with live wires and unwiped lips. Two species dominate the island's alleys and drains, but it is the larger, American (by way of Africa), beast that looms in the imagination with its bold forays, intrusive manners and unmatched ability to induce shudders as a barrage of spiny legs scrambles over furniture and unshod feet. The adults, which have been clocked sprinting at 5.43 km/h (or fifty body lengths per second), seldom, if ever, fly, but those that do inevitably add a new dimension of loathing to souls unused to the creeping underbelly of local nightlife. Even in death, there is little to us do part, for their crushed torsos and scattered limbs colour the floors of corridors and food courts each dawn, reminding us of the futility of efforts to banish their nocturnal feasts to levels that will never stain sensitive lines of sight.
Blattodeans also abound in local as well as antipodean woods, where they share the bark with earwigs and scorpions, forage on bushes alongside huntsmen and katydids, and worm through soiled layers of springtails and millipedes. The nymphs of one blaberid, Pseudophoraspis nebulosa, even dives into pools. Those living on the earth and under logs are dull wingless creatures, easily mistaken for a leaf blade or oblong piece of debris in a sea of dead, dry things, and instantly missed even when they break cover in a moment of vulnerability. But many forest roaches, in contrast to the dirty browns and dingy blacks of domestic vermin, often sport clean (if cryptic) patterns, coy peepers and a disposition that just borders on raffish charm. Like their household kin, most retain broad tegmina and a hood-like pronotum, which together form a flexible if flimsy shield that conceals the head and other fragile parts. One subfamily of blaberids has gone the whole hog, developing a tough integument and cuticular folds that allow the females and their nursing brood to safely turn their backs on would-be predators. Another genus, Prosoplecta, from the family Blatteridae, has refined this tactic to closely mimic distasteful ladybugs and leaf beetles.
Cockroaches were, indeed, lumped with beetles in times past, when they boarded freighters and frigates to find new homes in the warm nooks of industrial towns. The confusion is most often applied to a shiny, temperate, species that further misleads in its putative lands of origin, but has also led to the christening of an entire order after cucaracha, a Spanish chafer (the Germans, on the other hand, employ the delightfully onomatopoeic term 'Kakkerlak'). As late as the 1920s, commentators still made little effort to distinguish between the two, drawing attention instead to the insects' declared inclination to transform from friend to foe in the flats of unsympathetic hosts. The etymological muddle is not entirely inexcusable, as both groups bear hardened forewings and a conspicious, lumbering gait.
A slightly more surprising revelation is the recent merging of cockroaches with another tribe of pests: the termites. The fatal blow to Isoptera as a higher taxon came in the discovery of morphological similarities between termite nymphs and those of Cryptocercus, a xylophagus cockroach that also shares symbiotic gut fauna with primitive termites. Cryptocercus, which engages in extended bouts of biparental care that ensure the proctodeal trophallaxis of essential flagellates to the offspring, also offers a model for how eusociality could have arisen in a clade already predisposed to the formation of primitive colonies.
Other cockroaches exhibit varying degrees of sociality. The so-called German cockroaches that infest backstreets and bus seats emit a pheromone that acts as an aggregation signal, although the animals have not been shown to actively 'recruit'. The order also boasts a wide continuum of reproductive strategies: some females build nests, others perform brood care and transport, and not a few secrete the blattodean equivalent of milk for their nymphs. Some retain the ootheca at the genital opening like a half-extruded piece of shit, while a number practice false (due to the persistence of the oothecal membrane) as well as true ovoviviparity. One species, Diploptera, goes as far as to nourish its unborn young in a mammal-like manner. The aforementioned Cryptocercus, a complex of nine species, as well as two other genera, Salganea and Panesthia, live within rotting logs – environments that offer safety and stability but are nutritionally demanding and hence favour families who linger and pass on vital symbionts to altricial neonates.
For all their biological diversity and ecological intrique, Singapore's cockroaches, all 100 or so of them, native or otherwise, will probably never enjoy the regard accorded to prettier bugs. The handful who associate with man, like other maligned arthropods, will continue to find filthy niches even in this cleanest of cities. For the vast majority, restricted to damp understoreys or the canopies of broken woods, it suffices to have enough foliage, flowers and fungi to chew on, and adequate crannies on trunks and along trails in which to squeeze thin bodies and nurse new generations of little black beetles, the progeny of a particularly resilient branch of life that has survived Permian catastrophes and will likely persist after the human race burns out in a fit of anger at the inability of the planet to satisfy its needs and sustain a world of rank prodigality.
Reference: James T. Costa, The Other Insect Societies. William J. Bell et al, Cockroaches: Ecology, Behaviour, and Natural History.