The Book of the Aquarium/Part 3/Chapter 6
In the Cuvierian arrangement the land and water bugs stand between the true beetles and butterflies, and in those members of the order which possess wings, the chief characteristic is, that the anterior pair fold nearly horizontally, partly lapping over each other, and are of a leathery texture at the base. The majority of the members of the order are inhabitants of tropical climates, and some of them display colours equal to those of the true beetles. Not a few have the power of emitting powerful odours, in some cases of an agreeable nature, and in others—as the common bed bug—of a most disgusting nature. The order readily separates itself into two great divisions—namely, the Geocorisa, or Land Bugs, and the Hydrocorisa or Water Bugs. Both divisions supply a few specimens for the Water Cabinet, but the most important are those belonging to the second class.
Among the first class in this order the most interesting is Hydrometra stagnorum, or the Water-measurer, which may be seen treading the surface of still brooks and rank pools in summer-time, in company with swarms of tipulidan gnats (Chironomi), whirlwigs, and two other aquatic bugs, the Gerris locustris and the Velia currens of Latrielle. The Hydrometra is a lively creature, a body so slender as to be little more than a black line half an inch in length, from which the long and angularly-jointed legs proceed in regular pairs. Under the microscope the divisions of the body are very plainly and prettily marked, and the terminal processes of the legs are made after the model of those water-shoes with which a certain clever Norwegian lately undertook to walk on water with nearly as much ease as on land. Whether the mechanician ever succeeded in this enterprise is not on record, but it is on record in the Book of Nature that this, and many other similarly-formed creatures, have found on the aqueous element a safe flooring for their feet ever since the first hour of creation, ere He who equipped them, had sent his Son to walk upon the waves.
Notanecta and Nepa are of the same order, but are true water-bugs, formed for diving and sub-aqueous life. The Notanecta, or Boat-fly, is a rapacious creature, that spends much of its time lying in wait for prey, but which exhibits immense activity when it captures its booty, darting down with it, and holding it firmly by the fore-legs, which are formed as claws. It is ingeniously adapted for the predaceous aquatic life it leads; the general form is well adapted for propulsion through water, and the hinder legs have an oar-like form, and are fringed with bristles along the edge, by which their striking surface is much increased. The boat-fly is an artistic swimmer; it varies its motions considerably, and delights in swimming on its back, a feat in which it is aided by its eyes being so placed as to enable it to see both above and below, and thus gain early intelligence of danger, or of the approach of its prey. Owing to their liveliness and voracity, they afford much interest when domesticated, and should be treated as directed for Dytiscus.
The Water Scorpion is a good representative of the Nepidæ, and has the distinguishing features of its tribe very strongly marked. The Water Scorpion is a very common inhabitant of our brooks, and its singular form quickly arrests the eye of the sportsman when turning over the contents of the drag-net. N. neptunia and N. cinerea are, perhaps, the most common; and either of these is an admirable object for the microscope. The water-scorpion is the victim of the parasitic water-mite (Hydrachna abstergens), which inserts its egg in the body of the Nepa, and thus compels it to support the young of its worst enemy, a task which it performs at the cost of its life. I have several times introduced the Hydrachna into my jars of Nepa, but have never yet witnessed the parasitic deposit of the eggs. In confinement, the Nepa is the least hardy of any creature in the collection, if the sun strikes the jar it perishes, and it will not live long unless it has means of occasionally leaving the water—hence a broad jar should be used for it, and a small piece of pumice stone should be floated in it, to form an island on which the insects may take refuge.