CHIRO'NOMUS, a genus of Dipterous Insects of the family Tipulidce. This genus was established by Meigen, and is principally distinguished by the following characters :—Fourth joint of the palpus longer than the rest ; antenun 13-jointed, in the male, and furnished with long hairs ; the antennae of the female are 6-jointed, and the hairs are short ; the anterior legs are inserted at some distance from the others, and the anterior tarsi are generally very long ; the wings when closed lie parallel, and they have three posterior cells; the body is long, slender, and hairy.
Mr. Stephens, in his Catalogue of British Insects,' enumerates upwards of eighty species of this genus : they are all of small size, frequent marshy situations, and very much resemble gnats. The worm known to anglers by the name of Blood-Worm is the larva of one of the species of this genus—the Chircatontus plumosus. This worm is about half an inch in length ; the body consists of numerous segments, and is furnished at the tail with several appendages which constitute the breathing apparatus. It is seen during the summer months ou the mud near the edges of ponds and ditches ; when thus seen how ever it is only shifting from one place to another, its natural locality being in the mud, where it may generally be found in great numbers, living for the most part under water. This larva is much sought after and devoured by birds and fishes ; but (luring the summer of 1836 we discovered dud It had a very formidable enemy In an insect of its own order. A fly, which closely resembled the house-fly, wee observed in great abundance on the mud which had just been left by the retiring water, and we found them assembled in little groups of five or six, in the act of extracting the blood-wort-en from their holes, using the proboscis for this purpose : but no sooner was the worm fairly dislodged than a battle ensued, for each apparently wished to have the worm to itself; those that kept possession sucked out the fluids from the worm.
The pupa is of a brownish colour; the body is cylindrical, the head, thorax, wings, and legs are inclosed in separate sheaths, and, with the exception of the two fore legs, lie in a close and compact mass ; the fore legs, covered by their sheaths, project from each aide of the thorax. In this as well as in the larva state, the animal lives iu the water. The breathing apparatus consists of two appendages, one on each aide of the thorax, and each in composed of five branches which spring from a common centre.
When the insect is ready to quit its pupa case, it gains the surface of the water, and there remains suspended for some little time with, the disc of the thorax slightly protruded; this part bursts down the middle, and the insect, which is hairy, and hence does not easily wet, places its feet upon the surface of the water, where it floats (if the weather be calm) with the greatest safety. We observed, upon taking
one upon our finger, that the wings are at first opaque and white, and filled with a fluid ; but in a minute this fluid was expelled, and the aides of the wings collapsed and became transparent. The fluid thus ejected we perceived on-our finger beneath the insect, but could not ascertain from what part of the wing or body it made its escape.
Discussions have arisen on the means which this animal possesses of suspending itself at the surface of the water without motion, its specific gravity being supposed to be greater than water.
Messrs. Kirby and Spence account for it by • kind of propelling power which the centre of the thorax possesses, and state that this part being thus protruded and drying, the attraction of the air to the dry portion of the thorax is sufficient to overcome the slight difference in the specific gravity between the animal and the element; but it is further stated that if a drop of water fall upon the insect at this time it will immediately sink.
We have kept these insects in a glass jar for the purpose of observing their habits, and are very much inclined to doubt that the specific gravity of the pupa is greater than that of the water, at the time just previous to the transformation from pupa to the imago state. Indeed at this time it appeared that they could not keep from the surface, unless they were in motion. Whenever we approached the jar, being at the top, they immediately descended by a quick zigzag movement of the body; but upon our remaining quiet for a moment they ceased all motion and rose to the surface again. We imagine that at this time the animal within baying become partially disengaged from the pupa case, the space between the two in filled with sir, that this would be sufficient to overcome the difference of specific gravity between the animal and the water, and that there would most probably be more air in the region of the thorax than elsewhere ; and hence this part is protruded from the water.
The perfect insect is of a pale-ash colour, and is a little larger than the common gnat, which it resembles. This, as well as others of the genus, is remarkable for its habit of carrying the two fore )ego in a horizontal position ; they project in front, and might be mistaken for antenna; these latter organs however are very beautiful, and in the males resemble little plumes.