I was walking outside during a recent heatwave in Sydney, swatting all the newly hatched flies and contemplating how much of the Earth鈥檚 biomass is accounted for by insects, when it occurred to me that I have never heard of any insects that live in or on the sea. Are there any?
鈥� The only truly marine insects are the sea skaters of the genus Halobates, order Hemiptera. Lanna Cheng gives a full account of these in the Oceanography and Marine Biology Annual Review of 1973 (vol 11, p 223), while provides online information. This is updated in a 2004 paper. 鈥淭he marine insect Halobates (Heteroptera: Gerridae): biology, adaptations, distributions and phylogeny鈥� (vol 42, p 119).
Alistair Lindley, Sir Alister Hardy Foundation for Ocean Science, Plymouth, Devon, UK
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鈥� Marine insects certainly exist, although they only constitute a tiny percentage of the total number of insect species. The species range from those which live in brackish water, for example in saline lagoons and rock pools at the upper limit of the splash zone, to species which live on or beneath the sea surface.
A survey of brackish lagoons in Ireland recorded 77 species of insect, although most of these are not confined to the habitat. Flies (Diptera), beetles (Coleoptera) and true bugs (Heteroptera) were the commonest groups. The flies are usually present as larvae, the others in both the larval and adult stages.
True marine insects can be divided into species that live their entire lives on the sea surface and species that can tolerate immersion either as adults or as larvae.
The five species of sea skaters (Halobates) are examples of the first group and are often cited as perhaps the most extreme example of marine insect (top photograph). It is true they never voluntarily venture onto land, but they actually only live on the water surface without getting wet 鈥� just like pond skaters and water striders (bottom photograph), their freshwater fellow member of the family Gerridae. Halobates lay their eggs on flotsam and jetsam. They can be found in all the world鈥檚 oceans between the latitudes of around 40掳 north and south.
Arguably, species such as the true bug Aepophilus bonnairei, an inhabitant of rocky Atlantic shores of western Europe and north Africa, are more truly marine because they can survive regular and prolonged immersion in seawater.
At high tide, adult and larval Aepophilus shelter in rock crevices or in the holes drilled by rock-boring molluscs. They emerge at low tide to feed, searching for prey in seaweed. Aepophilus tends to be most common on the lowest part of the shore and therefore spends most of the tidal cycle under water. Consequently it is more often seen by marine biologists than entomologists.
Brian Nelson, Portadown, Armagh, UK