AQUATIC HABITATS
The so-called aquatic or amphibious cockroaches are all members of the subfamily Epilamprinae (Chopard, 1938). These forms are not nearly as aquatic as water beetles or aquatic Hemiptera, but in their relations to water they behave differently from nonamphibious cockroaches, which tend to avoid water except for drinking. There are apparently no special morphological characteristics that distinguish amphibious cockroaches (Shelford, 1907, 1909a; Chopard, 1938), although Takahashi (1926) listed several characters that he considered made Opisthoplatia maculata adapted for an aquatic life: (1) Back of body easily wetted; (2) long hairs on underside of thorax trap air; (3) terminal abdominal spiracles open into tubes that extend rearward; (4) long hairs on ventral surfaces of cerci "protect" terminal abdominal spiracles. Annandale (1906) also suggested that the position of the posterior abdominal spiracles, at the base of tubes that project rearward from beneath the seventh tergite, are an adaptation to an aquatic life. However, as Shelford (1907) and Chopard (1938) have pointed out, this same feature may be observed in many terrestrial cockroaches. The legs of amphibious cockroaches are similar to those of nonaquatic species and are not modified for swimming (Shelford, 1909a; Takahashi, 1926).
Biological observations have been made on relatively few species, but representatives of at least six genera occur in quasi-aquatic habitats. Strictly speaking, these cockroaches live on land at the edges of streams or pools and spend relatively brief periods in the water. A few species are found in water-filled bromeliads. The behavior of the known amphibious species of cockroaches in relation to their habitats is discussed below.
AMPHIBIOUS COCKROACHES
Audreia bromeliadarum
Panama.—These insects when disturbed would dive into the water that had collected in the base of the bromeliad; they would disappear beneath the surface and remain submerged for some considerable time (Caudell, 1914).
Dryadoblatta scotti
Trinidad.—This species was taken from the leaf bases of Tillandsia sp. at 3,100 feet; water had collected between the leaves and the insect was presumed to be more or less amphibious (Scott, 1912). Subaquatic in the bromeliad Glomeropitcairnia erectiflora: "This large and handsome species [D. scotti] is very common in the larger, water-filled, epiphytic bromeliads of the rain forest. Within these plants it is usually to be found, often in considerable numbers, just above the surface of the water or partly immersed in it. The cockroaches will descend rapidly into the water when alarmed and probably obtain their nourishment from the accumulated organic matter in the water. Floating material is probably taken and it seems less likely that they feed below the surface. They appear to be ovoviviparous." (Princis and Kevan, 1955.)
Epilampra abdomen-nigrum
Puerto Rico.—Abundant in wet "malojillo" meadows. The nymphs swim easily and remain under water for long periods, as do the adults (Seín, 1923; Wolcott, 1950).