Social Wasps." Pop. Sci. Mo., 61: 339-351, 1902.

The Biology of the North American Crane-Flies

(Tipulidæ, Diptera)

V. The Genus Dicranoptycha Osten Sacken

BY CHARLES P. ALEXANDER, Ph.D. (Cornell)

GENERIC DIAGNOSIS

Larva. Form very elongate, terete; integument smooth, glassy, transparent; abdominal segments two to eight with a basal transverse band or area of microscopic chitinized points on the ventral surface; segment eight with a similar band on the dorsum. Spiracular disk surrounded by four lobes, the lateral pair more slender than the blunt ventral pair; dorsal lobe very low or lacking; spiracles small, widely separated; a triangular brown mark on the disk between the spiracles; anal gills a fleshy protuberant ring surrounding the anus. Head-capsule compact, massive, the præfrons large with a few marginal punctures; externo-lateral plates very broad. Labrum large, flattened, pale; antennæ two-segmented, the apical segment almost as long as the basal segment, narrowed to the blunt tip; mandibles with a blunt dorsal and two blunt ventral teeth; maxillæ generalized in structure; hypopharynx a rounded cushion; mentum deeply split behind but not completely divided, with three principle teeth and a small lateral tooth on either side.

Pupa. Cephalic crest low, depressed, setiferous; labrum tumid; labial lobes oval, contiguous; antennal sheaths ending opposite the base of the wing. Pronotal breathing-horns microscopic, represented only by tiny triangular tubercles; mesonotum unarmed; wing-sheaths ending opposite the middle of the third abdominal segment; leg-sheaths ending opposite the base of the fifth abdominal segment, the tarsi terminating on a level, or nearly so. Abdominal tergites and sternites each with four transverse rows of microscopic setæ; lateral spiracles on segments two to seven.

DISCUSSION OF THE GENUS

The genus Dicranoptycha was erected by Osten Sacken in 1860 (Proc. Acad. Nat. Sci. Phila. for 1859, p. 217). The genus includes a small group of crane-flies with a Holarctic distribution, there being about six species in North America and two, or possibly three, in Europe. As I have indicated elsewhere, D. signaticollis v.d.W. of Java is undoubtedly a species of Libnotes. Of the American species, D. germana O.S. is characteristic of the Canadian life-zone of northeastern America. D. sobrina O.S. is widely distributed in the United States and southern Canada, usually occurring in the Transitional and Upper Austral life-zones. So far as known at present it is the only species of the genus occurring on the Pacific slope. The remaining American species (nigripes O.S., winnemana Alex., tigrina Alex. and minima Alex.) are Austral in distribution, occurring in the southeastern and south central United States. A more detailed account of the distribution of the species is given in another paper by the writer which may be consulted (Proc. Acad. Nat. Sci. Phila. for 1916, pp. 496, 497). All of the known species are generally similar to one another in appearance and are separated by relatively slight differences of size, color and structure.

Nothing has ever been written concerning the immature stages of this peculiar group of crane-flies. The species described hereinafter were reared at Lawrence, Kansas, and the general conditions under which they occur may be briefly discussed:

North Hollow, on the Campus of the University of Kansas, is a typical dry Austral woodland traversed by a small stream that is entirely dry during the months of midsummer drought. The soil consists of a rich black humus that is soft and mellow except during the period of greatest dryness, being overlain by a varying depth of vegetable debris and leaf-mold. It is in this relatively dry soil that the larvæ of Dicranoptycha occur. The forest cover consists of Carolina poplar, Populus deltoides Marsh; black walnut, Juglans nigra L., white elm, Ulmus americana L.; Kentucky coffee-tree, Gymnocladus dioica (L.) Koch; honey locust, Gleditsia triacanthos L.; red bud, Cercis canadensis L.; yellow wood, Cladrastis lutea (Mx.f.) Koch; tree-of-heaven, Ailanthus glandulosa Desf., etc. The principle shrubs are the goose-berry, Ribes gracile Mx.; poison ivy, Rhus Toxicodendron L.; wahoo, Evonymus atropurpureus Jacq.; bladder-nut, Staphylea trifolia L.; coral-berry, Symphoricarpos orbiculatus Moench.; blackberried elder, Sambucus canadensis L., etc. The herbage is made up of tall grasses, composites and, in the spring, the all-dominant cleavers, Galium. In addition to the above, great tangles of lianas (Smilax, Vitis, Ampelopsis, etc.) are found.

In situations such as the above these Austral species of Dicranoptycha spend their entire lives. The first larvæ of D. winnemana were found here on March 20, 1918, by the writer and his wife. At this time they were well grown (length 16 mm.; diameter 0.9 mm.). They occurred just beneath the cover of fallen leaves and other debris in the upper layers of soil. Here they were associated with pupæ of Tipula angustipennis Lw., larvæ of Sciara (Mycetophilidæ); Psilocephala hæmorrhoidalis Macq. (Therevidæ), numerous beetle larvæ, centipedes, etc. By their elongate form and glabrous shiny skin they are very characteristic and easily recognized. The glassy appearance of the body suggests the shiny shells of a small coiled molluscan whose dead fragments occurred in some numbers in the same situations. These larvæ were placed in rearing and the first adults appeared in the breeding-cages on May 6, and from that time on continued to appear in large numbers. It was over a month later that the first individuals were taken in the field. The pupal duration could not be determined closer than ten days, and this may be the usual length of time required for this stage. The first larvæ of D. minima were found on July 2, 1918, in similar situations in North Hollow. At this time they were only about one-half grown. On July 11 much larger larvæ of this species were secured and placed in rearing, emerging as adults on July 21. The larvæ, like these of D. winnemana, live just beneath the layer of leaf-mold in the upper zone of black soil. They are usually quite sluggish in their motions but at other times are quite active. The larvæ are herbivores and feed on the rich organic earth in their haunts. When ready to pupate, they encase themselves in earthen cells (10 mm. × 3.5 mm.), firm in texture, rather thick-walled but without silk. There is a small opening at either end. The length of the cavity is but little greater than the pupa itself. In this cavity the pupa rests and matures. As in other insects, the teneral pupæ are very pale yellow but gradually darken in color until, at emergence, they are of a dark brownish-black. When newly transformed the teneral flies rest on the ground and on the leaves of low plants nearby.

The adult flies of D. germana usually occur in the immediate neighborhood of running or stagnant water and may be swept from the rank vegetation in such places. The flies rest on the upper surface of the leaves of tall herbs and low shrubs. In eastern Kansas, the flies of D. winnemana, D. tigrina and D. minima often occur together. In June, D. winnemana appears on the wing and is found associated with Tipula morrisoni Alex., T. mingwe Alex., etc.; in July, D. minima appears, together with Tipula flavibasis Alex., T. unimaculata Lw., etc.; still later in