20 AQUATIC INSECTS. 



remarkable while the various methods of locomotion and of secur- 

 ing an air-supply are truly wonderful. 



There is not a single order of insects in which all the species are 

 aquatic throughout larval and adult life. There are several orders 

 in which all the larval forms are aquatic. May-iiies CEphemerida), 

 Stone flies (Plecoptera), Dragon flies (Odonata) and Caddis flies 

 (Trichoptera) are all aquatic in the larval stages, whereas the 

 adults are serial. Several families of Hemiptera and Coleoptera 

 are aquatic throughout larval and adult life, whereas many 

 Neuroptera, a few rare Lepidoptera, several large families as well 

 as many widely scattered sj)ecies of Diptera are aquatic during 

 larval life. And in the Hymenoptera, one of the most highly 

 specialized of all orders of insects, aquatic forms are found. But 

 few of these have been studied. They are all parasitic, either on 

 aquatic larvae or eggs of aquatic si^ecies. These remarkable 

 insects swim either by means of their legs or wings. To see some 

 of these minute imrasites swimming through the water, using 

 their wings as organs of locomotion, is one of the most wonderfu.1 

 sights imaginable. Undoubtedly many species exist, and if more 

 entomologists were to devote their attention to rearing aquatic 

 insects many new species of these parasites would be discovered. 

 At the present time only ten aquatic Hymenoptera are known, 

 two of which are common to Europe and America. 



As all insects were originally terrestrial those that have assum- 

 ed aquatic life were forced to it either through severe competition 

 on land or by a more available food supjily in the water. Prov- 

 ision had to be made for an air-supply. Aquatic organisms may 

 obtain their air-supply either by coming to the surface to breathe 

 or by making use of the oxygen dissolved in the water. The 

 common method of securing air dissolved in the w^ater is by means 

 of blood gills which are rare among insects, being found in but a few 

 scattered forms. The common methods are either by the use of 

 tracheal gills, thin membranous extensions of the body- wall in 

 which there are numerous small trachea, or by the insects coming 

 to the surface to secure air directly by means of open spiracles. 

 Some aquatic forms which live in swift streams possess no respira- 

 tory organs, securing their air supply directly through the thin 

 body- wall. 



As this short i^aper does not claim anything new or original it 



