The Sea-Midge and its Larva

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THE SEA-MIDGE AND ITS LARVA.

THE SEA-MIDGE AND ITS LARVA.

BY CLAUDE MORLEY, F.E.S., F.Z.S., DESPITE the fact that the Insecta " is, beyond

&c. all comparison, the most populous Class of animals, embracing as it does more than ten times as many species as all other living beings put together, the sea is singularly destitute of them. It has been frequently said that no true Insect is marine ; and, though this is not literally true, the minuteness of the exception makes the rule even more striking than it would have been if absolutely universal. Of the hundreds of thousands of Insects known to exist, but two live in the sea, and both of these may be found on our own coasts. However there is, besides these, the larva of some two-winged Dipterous fly, which is marine.

I have repeatedly taken it on our southern shores, quite out of the influence of fresh water," wrote Philip Henry Gosse some eighty years ago (Manual Marine Zoology 1855, i, 178), lucidly exhibiting the extent of knowledge upon the subject at that period. His Fly was not the present Midge ; for he adds (lib. cit. ii, 217) its description.

Our Midge rejoices in the name Thalassomyia Frauenfeldi Schiner ; and the earliest specimens of it noted in Suffolk were two males, taken by me on the sea-beach at Dunwich upon 9 September 1921. These were presented to the National Collection, whence Mr. Edwards recorded themfirstfrom " Suffolk " merely, Cornwall, Devon and Somerset alone in Britain, during 1929 (Trans. Ent. Soc. lxxvii, p. 371). Fora decade no more were observed here ; tili a great number occurred to me, running just at high-tide mark erratically and excitedly over the green sea-weed [Viva laduca, Linn.) that was interspersed with, small Barnacles (Baianus balanoide Linn.), growing on the vertical timbers of a large breakwater, on Gorleston beach at dusk of both 6 and 7 May 1931. When boxed, the female sits quiescently; but the male runs about actively, with its wings half-spread, making jumps rather than flights of no more than an inch in length. Our Member, Mr. Ellis, had already noticed a Midge in the same Situation, as well as a reddish larva under Viva that he expected would prove to be its immature form ; the latter seemed to be present just below high-water mark all the year round, as was especialy observed in November. Early in the following September he was so good as to give me several of these larvse, along with mature T. Frauenfeldi, thence for description.

THE LARVA (somewhat immature) is subcylindrical and but slightly attenuate towards the anal extremity, apodous and with out apparent setas, olive-green when in Chlorospermeous algae, but pink when in Rhodospermeous, and subtranslucent with thirteen segments. Two first segments

THE SEA-MIDGE AND ITS LARVA.

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corneous, opaque, evenly convex and slightly longer than broad ; head shining and chestnut-brown, apically truncate across the mandibles, with a pair of eyes upon each side ; second segment albescent-green. The five following segments gradually increasing in relative length from the strongly transverse third, and all bearing a broadly explanate lateral plication. Eighth to twelfth segments discally as long as broad. The anal one corneous, opaque and chestnut-brown.

Living free, among Algae wherein it rapidly retreats upon the approach of a shadow or any threatened danger, presumably from wading birds or insectivorous marine animals. Length, as described, mm.

Schiner did not know the larva (Fauna Austriaca, ii, 596) ; which is obviously quite unlike Campontia cruciformis, Jhnst.

(Zool. Journ. iii, 325), thought by Theobald to be the immature form of this Midge (Brit. Flies 1892, p. 202) and still queried as being such by Edwards (Trans. Ent. Soc. 1929, p. 371).

Chevrel's description of the larva of his synonymous Scopelodromus isemerinus (Arch. Zool. 1903) is inadequate ; nor is his larva contained in the British Museum. In fact, our SeaMidge has but quite recently been confirmed as British ; it was unknown to both Mr. Atmore and me in the Eastern Counties so lately as 1915 (Trans. Norf. Nat. Soc. x, Suppl. p. 16).

Theobald in 1892 and both Verrall's Lists of 1888 and 1901 regard it as doubtfully British; and the Chironomid referred to, though not named, by Furneaux (Sea Sbore 1903, p. 301) is obviously the same as Gosse's of 1855, above. Midges, in contradistinction to stouter Flies, are rarely seen upon seaweed ; and Thalassomyia is easily recognised there by its peculiarly nigrescent wings that are darker than those of any other Chironomid I know, its body-length of four mm., hind-leg length of seven mm. and alar expanse of about 7 | mm. ; it has been described as lacking any definite ornamentation, but actually both tegulae and halters are conspicuously primrose-yellow, or in cabinet specimens dirty-white, and the body is covered with very sparse elongate hairs, which on the occiput and sides of thorax become close grey pubescence.

Our knowledge of Midges has considerably advanced since Gosse's time ; several different sorts, smaller than Thalassomyia, occur upon European coasts including Madeira and our own ; Agassiz found " larvae of a species of Chironomus quite common off shore from the northern coasts " of America (Cruises of the Blake, i, 179) ; C. oceanicus at a depth of twenty fathoms there ; and Packard discovered both larvae and pupae of the genus in the salt-water of Clear Lake in California. Truly, as Edward Newman demonstrated, insects are ubiquitous ; from below the surface of the earth to high above the tallest trees, and their powers of adaption no less than wondrous.