Insects, other than water-striders that surf on the open ocean and lice that suck the blood of seabirds and diving mammals, occupy a marginal position in marine ecosystems, where they are probably outflanked and kept at bay by the crustaceans that have long conquered every aquatic niche and more than match the Hexapoda in diversity of function and form. What passes for marine insects are largely confined to saltmarshes, mangroves, tidal pools, beaches and rocky shores, peripheral habitats shared and contested with isopods, beachfleas, coenobitids and brachyuran crabs that have learnt to roam beyond the surf but still regard the sea as an ally, a refuge, a nursery, a womb that restores and repossesses the spawn of its podigal children.
For arthropods too far removed in time to embrace the sea without a storm of misgivings, the littoral zones offer the worst of both worlds, a trade-off between the bounties of the deep and the safety of the shallowest end, an environment at once too wet and too dry, too forgiving and too demanding, where the ability to swim or fly is outweighed by a penchant for staying low, hanging tight and making the best of the hours between the tides. Insects have done fairly well in wetlands, but most adaptations for breathing in fresh water, such as spiracular tubes and regular trips to the surface, falter when the waters are too high and rocky for bugs to tap on the air supply. Intertidal insects thus rely on cutaneous respiration or gills called plastrons to survive as larvae; adults take to the wing or hide in cracks, recesses and shells offering pockets of air and protection from the waves.
Marine insects tend to be minuscule and fugitive, so encounters with the order during forays to reef and flat probably deserve more scrutiny and less dismissal as wayward explorers or victims of rogue winds. One such sighting took place at daybreak on the eastern fringe of Lazarus Island more than two years ago, en route to a lagoon built to be forgotten. A small beetle, little more than a third of an inch long, crept about a damp rock, in the company of nerites and periwinkles, with no sign of distress or displacement. The beetle was no stunner, but it was still a pretty thing with a black-blue lustre on its elytra and orangey basal antennae segments. The find was shot and stored until recently, when a smarter eye pointed to a genus named after the father of Oedipus, King of Thebes. Laius, which occurs from east Africa to the Asia Pacific, belongs to a family of coleopterans commonly referred to as soft-winged flower beetles, as terrestrial representatives usually feed on pollen and pollinators as adults.
Enlarged second antennae segments are male hallmarks of a number of malachiids, so the beetle was probably a female and superficially matches the description of Laius flavicornis, which has been recorded from the coasts of Java, Sarawak and China. The genus has been observed on rocky shores, under stones on beaches, and on "the surfaces of reefs" and other substrates subject to tidal inundation, and one species, aptly named submarinus, is said to inhabit "cracks and holes of sandstone that reach pretty far out into the sea, quite covered during the flood-tide but dry during the ebb." The beetles, which are likely to be scavengers or predators of other intertidal arthropods, evidently have ways of coping with periods of submersion, which they can endure for up to 30 hours, and colonising oceanic isles, on their own power or by clinging to natural rafts. But the secrets of these maritime midgets are still largely out of reach and lost in translation – cyphers on the margins of two worlds and nodes in the tree of life that will remain in bud until curiosity blooms and stirs a much closer look at what moves these bright little bodies on the thin edge of the blue.