September, 1901.] 



KNOWLEDGE. 



195 



buzzing around his head. Tho individuals of some one 

 kind often occur in countless numbers, and when tlie 

 fli:?s, now somewhat neglected, have been thoroughly 

 studied, it is likely that their species will bo found to 

 exceed in number those of any other insect-order, not 

 excepting even the beetles. Certainly the naturalist who 

 £;oes to look for insects by the sea-shore in summer-time 

 will first of all be struck by the great abundance of 

 vai-ious kinds of flies. He needs not to search for them, 

 as for beetles or springtails, beneath stones ; they fly and 

 run to and fro in the sunshine with ceaseless activity. 



Among these insects the remarkable modification of 

 the wings of the hind pair into small stalked knobs or 

 " balancers " [haheref) leaves the fore-wings alone 

 functional as oi-gans of flight. This character marks the 

 flies as a vei-y distinct order of insects, and suggests for 

 them the expressive name of "Two-wings" (Diptera). 

 In many points of structure flies are the most highly 

 organised of all insects, and their great specialization of 

 form is mat<:hed by a gi'eat complexity in the transforma- 

 tions that they undergo. The most highly developed 

 members of the order begin life as degraded, headless, leg- 

 less maggots. The skin of the full-fed maggot hardens to 

 foi'm a brown, egg-shaped puparium, within which fii-st 

 the pupa and then the perfect fly is built up by a pro- 

 found dissolution and reconstruction of the larval 

 tissues and organs. The despised housefly and blue- 

 bottle are proclaimed therefore by their structure and 

 life-history to belong to the highest aristocracy of the 

 inscct>world. 



Out in the open air one may meet with many 

 hundreds of different kinds of flies more or less related 

 to om- well-known guests just mentioned. A vast 

 number of these, which differ from the blue-bottle and 

 its immediate allies in the absence of the silvery scales 

 at the base of the wings, are often spoken of collectively 

 as the " Acalypterata." Quite a little assemblage of 

 these insects haunt the shore just above high-water mark, 

 finding in the cast-u]) seaweed a playground for them- 

 selves, and a feeding-place for their offspring. They are 

 very nearly related to the bright yellow, hairy, red-faced 

 flies of the genus Scatophaga, which may be observed 

 any sunny day in vast numbers hovering over dung- 

 heaps. Fucellia fticorum (Fall.), the closest ally of 

 Scatophaga among them, is a small, inconspicuous ashy 

 fly, common on our coasts, and ranging along the 

 western and southern edge of the Continent from 

 Norway to the Adriatic. One other species of Fucellia 

 inhabits our shores, but there are seven or eight 



Fig. 1. Fig. 2. 



Fig. 1. — Coelopa pilipfs, male. ilai;ui6ed 3 times. 

 Fig. 2.— Orygma luciuosa, male. Magnified 3 times. 



different kinds known from the far north of the 

 Scandinavian peninsula — Lapland and Finmark. The 

 flies belonging to Coelopa (Fig. 1) and its allied genera 

 have a most characteristic aspect with their narrow. 



angular heads, small eyes, aud flattened, depressed 

 bodies. They all have stout and powerful legs, which 

 in some species are armed with a most formidable array 

 of spines, while in others they arc clothed with a dense 

 setting of long, woolly hairs. The distribution of 

 Coelopa is remarkable. Five or six species inhabit tho 

 British and Irish coasts, of which most have been traced 

 to Scandinavia, but only one or two range southwards 

 to Holland and Heligoland, so that the genus is 

 charact-eristically north-western. Of similar distribution 

 and habits is Orygma /iirtunm, Meig. (Fig. 2), a some- 

 what larger fly than the Coclopae, and distinguished 

 from them by its broad, rounded head.* Artorn 

 aestitum, Meig., is a still larger fly of an ashy grey 

 colour, less differentiated from related insects than are 

 its comrades of the soa^shore. It is of especial interest 

 since its grub has been described, t and proves to be a 

 greyish maggot with wrinkled skin, fourteen prominent, 

 conical, flesliy processes sunouiiding the air-openings at 

 the tail-end. 



This as.somblage of flies, some of whoso leading 

 members we have briefly sketched, though few in 

 species, is often vei'y numerous in individuals. On a 

 sunny day, when the tide is high, the observer has but 

 to lie on the beach to watch the ceaseless darting flight 

 of the insects over the seaweed-heaps. Many of tho 

 flies follow the receding waves, so that at low-water they 

 may be seen running over the recently exposed rocks 

 or alighting after a short flight on the still damp 

 seaweed. 



Many very small flies, belonging to the samo great 

 group as those just considered, but to a most distinct 

 sub-family, the Ephydrina?, also haunt the searshore. 

 As usual, a transition can be traced from marsh- 

 dwelling species to those which cling to the tidal 

 margin. Thus the tiny Alissa pygmaea, Halid. lives in 

 salt marshes. Tichomyza fusca, Macq. is found both 

 on chalky coasts at high-water mark and in the sewers 

 and outhouses of large towns, its grub feeding on decom- 

 posing limy material. Glenanthe ri/ricohi, Ilalid. (Fig. 3) 



Fig. 3. Fig. 4. 



Fig. 3. — Glenanthe ripicola, male. Magnified 8 times. 

 (After Ualiilay.) 

 FlO. 4. — Ckersodromia arenaria, male. Magnified 12 times. 



dwells on muddy sea^coasts, while nearly all our native 

 species of Scatella live among the seaweed masses 



• SeeJ n Sehiuer. " Fauna Austriaea, Diptera." Wien, 1861-4. 

 F Walker [Si A. 11. Ilaliday]. "Insecta Britanni^a, Diptera ' 3 vols 

 London, 1851-(5. Q. H. Vcrrall. " A List of liritisli Diptera. 



London, 1888. ■»«■ • i> 



t H Gadeau de KerviUe. "Notes sur les Larves Marines d un 

 Dipttr;.- Ann. Soc. Ent. Fr. (Vol. LXIII.), 1894, pp. 82-5. 



