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Home > Exyra ridingsii Riley

Exyra ridingsii Riley

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From Pitcher-Plant Insects II by FMJ (Entomological News Dec 1907) and unpublished notes. Distribution (1892-1926) (See Map)

Sarracenia flava

Sarracenia drummondi

Food plants

Habitually, E. ridingsii feeds on S. flava, occasionally S. minor. However, in captivity, E. ridingsii thrives in other species, even S. purpurea, and probably occurs in any Sarracenia within its geographical range.


Egg—﻿Low dome-shaped, flattened circular base; diameter, 0.83mm; height, 0.62mm; from near the apex radiate twelve to fifteen broad shallow grooves, which fade out before reaching the greatest diameter near the base; white unpolished, thickly and finely reticulate the bottoms of the minute depressions (in living eggs) pale green, as though the raised white reticulations formed an opaque crust like surface overlying the translucent shell. Deposited singly on the inner walls of the pitchers of (preferably) Sarracenia purpurea. See image to the right.


Stage I—Pale brown, polished and glistening, tinged with purplish-red segments on the swollen bases of the larger tubercles; intersegmentally paler, the segments deeply cut, and those posterior to A4 paler and more translucent; an indistinct and narrow pale dorsal line; tubercles low conical, denser brighter brown, well defined and contrasting.

Head rounded, bi-lobed, smooth and polished, brownish-amber; only primary setae present on head and body; width of head, 0.48mm.

Segment T1 with a roughly crescent-shaped cervical shield bearing 8 setae (alpha, gamma, beta, delta); from this, tubercles epsilon and rho are separated and partially fused, the seta arranged horizontally; kappa and eta are arranged vertically, their tubercles fused (the prespiracular wart); two setae of the pi group, from a fused tubercle (the subventral wart).

Segments T2 and T3 with setae alpha, beta, epsilon, and rho (1a, 1b, 11a, 11b) in a vertical line, beta from the largest of their low conical tubercles; below these are kappa, from a large tubercle, and pi, each unisetose.

The abdominal segments bear the usual primary setae on similar low conical tubercles; on segments A1, 2, 3, and 4, tubercles rho and kappa (iii and iv ) are almost in contact, their otherwise circular bases usually flattened by near confluence.

Suranal plates brown, chitinized, bearing 8 strong setae; ventral prolegs on segments A5 and A6; legs and prolegs brown. Total length at hatching, 2.6mm.

Stage II—Smooth and shining as before, though generally darker and more heavily pigmented, and some examples tending more strongly toward purplish-red; head 0.66mm.

On segment T1, tubercles epsilon and rho are fused; on T2 and T3, theta appears as a small tubercle caudad of kappa; kappa is very considerably enlarged, and bears an additional fine seta from a papilla upon its base (eta?), ventrally. As usual in this instar, tubercle mu appears upon the abdominal segments; on segments A1, 2, 3, and 4, the dorsal tubercles alpha and beta (I and ii) are much enlarged, and their apices are surmounted by a ring of microscopic spines surrounding the base of the large seta; on these four segments, kappa (iv), of similar structure is still larger, approaching the size of "lappet" condition of the later stages; on the remaining abdominal segments, all these tubercles are of moderate size, though the tubercles generally are higher than before, with at least their apices black.

Stage III—Texture not so shining and polished, and brown tones usually prevailing, to the elimination of the reddish-purple; head width, 1.1 to 1.2mm; occasionally the traverse bands across the head, present in succeeding instars, are faintly indicated on the usually uniform brown ground; the "lappet" tubercle, kappa (iv) on segments T2 and 3, A1, 2, 3, and 4, is still further enlarged, and on these four abdominal segments is borne on a swollen fleshy base, with rho (iiii) on the cephalo-dorsal surface, the spiracle ventrad of rho; the enlared tubercle, kappa, is shortly and sparsely spined from base to apex; and as in the preceding instar, the dorsal tubercles, alpha and beta, on A1, 2, 3, and 4, are much larger than these tubercles on succeeding segments.

Stage IV —The characteristic color pattern of the head, as described in t he next instar, is now visible, but usually without as great contrast between the ground color and that of the bands, as in the next molt; head width, 1.5mm; in comparative size and arrangement, the tubercles exhibit little change, but the sparse setosity of the "lappet" tubercles (kappa, or iv) is stronger, and extends microscopically over the higher portions of the segments as well.

Stage V (last larval instar)—Dull coffee brown to vinous brown or dull purplish-red; intersegmentally paler, almost white, contrasting; to the naked eye smooth, but microscopically with a short sparse spine-like pubescence.

Head width 1.9 to 2.1mm; head strongly bi-lobed, epicrania rounded; the front high, reaching more than midway of the epicrania, which are smooth, glistening, china-like, in ground color varying from almost white to pale coffee brown; a narrow vertical band of dark brown extends from the base across the vertex of each epicranium, enclosing seta i, just beyond which it terminates abruptly; ventrad of this, on the light ground, is a small rounded dark brown spot (sometimes obsolete); setae ii and iii enclosed by a broad horizontal band of dark brown which extends completely across the head, crossing the adfrontal sclerites at their junction; on each epicranium, opposite the adfrontals ii, but usually not reaching the frontal sutures, a short horizontal brown bar of irregular shape, enclosing the head setae iv and viii; the region about the eyes, the clypeus, thence dorsad narrowly along the frontal sutures, pale brown; eyes and antennae black.

On segment T1 the cervical shield—in the first instar plate-like, in the succeeding molts more and more tuberculate—consists of the fused bases of the eight setal prominences, a media furrow dividing it into two parts; the tubercles forming the plate are dark amber colored, the apices black; on T2 and T3, the larger tubercles are obviously, though sparsely spinose, beta (ib) being by far the larger of the dorsal series, and compared with semicrocea, on the thoracic segments, kappa is much higher and more conspicuous. On segments A1, 2, 3, and 4, the dorsal tubercles are large, well chitinized and spinose; the lappet tubercle, kappa, is slightly above the level of the spiracle, bears rho (iii) on its enlarged base, its spiny covering is shorter than in semicrocea, and the "lappet" is proportionately more slender, firmer in texture and more chitinized, than in the corresponding stage of semicrocea; epsilon (iiia) is inconspicuously present; on A1, the tubercle pi is bisetose, with obviously only partial fusion while on A2, 3, and 4, it is plainly trisetose; on segments A5, 6, 7, and 8, the large tubercles of the preceding segments are much reduced, the "lappet" condition not existing, and rho and kappa are well separated, the latter falling to or slightly below the level of the spiracle; on A7 it is far below, close to eta; the dorsal tubercles are enlarged on A8 and 9, but are not as large as those on the first four abdominal segments; the spiracles are dull ferruginous, that on A8 considerably enlarged; the feet are black, the prolegs dark brown; prolegs present on abdominal segments 5, 6, and 10; crochets in a uniordinal mesoseries.

The head-pattern is fairly constant, except that individually the width of the brown bands is quite variable, resulting in their wider separation or their occasional fusion. The total length, before pupation, is about 30mm. Pupa—﻿Length, excluding caudal setae, 14 to 17mm. Pupal cuticle not heavily chitinized, thin, flexible, the paler examples sufficiently transparent to exhibit the color pattern of the imago. Color varying from almost uniform pale amber to dull dark mahogany brown, the pupae of the summer broods usually of the paler form. Front strongly and acutely produced over the head, the protuberance shaped like a liberty cap. Prothorax of moderate length; epicranial suture present; labial palpi indicated by a slit-like separation of the maxillae, narrowly in contact with the labrum. Mesothoracic wings extending to the incision between the fourth and fifth abdominal segments; metathoracic wings dorsally visible to the fourth segment. Maxillae and mesothoracic legs of about equal length, extending almost to the caudal margin of the wings, where a small portion of the metathoracic tarsi is visible. Antennae shorter, terminating opposite the incision between the third and fourth abdominal segments. The mesothoracic legs do not reach cephalad to the eye-pieces; prothoracic tibiae narrowly visible. Dorsal cephalic margins of abdominal segments five and six with strongly marked striations; dorsal caudal margins of segments four and five strongly punctate. Caudal end of body with two long straight setae and a few shorter slightly hooked setae; all the others fine, pale, very inconspicuous and difficult to locate except under the compound microscope.

Imago—﻿Male and female; expanse, 24-31mm; average expanse 30mm; colors, black and yellow.

Head—﻿vestiture dense, hairy, brownish black, hiding the pointed tubercular projection of front and the black slightly elevated ocelli; antennae pale, closely scaled above, finely and shortly ciliate below, the joints scarcely distinguishable; length of antennae, about 8mm; of tongue, 7mm; first and second joints of palpi with long shaggy hair-like scales, those of the small third joint much finer and more closely applied; palpi black, the second joint tipped with yellow, the inner surface of all joints pale.

Thorax—﻿convex, uncrested, clothed with rather long hair-like scales; collar, anterior portion of patagiae, and thorax to center, rich velvety brown; the remainder (except in the suffused forms) clear and yellow.

Legs—﻿strength, hairy; tarsi and spurs pale dull yellow, in the darker forms with some admixture or suffusion of gray; for tibiae brownish black to sooty black, tipped broadly with clear yellow, which may be partially obscured in the dark forms; middle and hind tibiae varying from almost clear yellow to brownish black, each with one dark band.

Wings—﻿costa of primaries arched, apex rounded, approximately the same width as the primaries. Examples with the markings well defined are as follows: ground color of primaries, clear straw yellow; from a basal line extending from costa to cubitus, and a transverse anterior line extending from costa, outwardly oblique and almost straight to inner margin, deep velvety brownish black; this somewhat comma shaped dark band is consequently broad and subquadrate from costa to cubitus, thence narrow and equal to inner margin; thence to the median line, clear yellow; the dark median line varies from narrow to very broad, often outwardly diffuse, slightly to strongly arched, but reaching interior margin about opposite its inception on the costa; reniform, when visible, a poorly defined shallow yellow crescent in the transverse posterior line, yellow, often considerably obscured by dark scales; transverse posterior line arched and almost parallel with the median, narrower than median, and reaching the interior margin slightly nearer the median, than on the costa; beyond the transverse posterior line, sometimes narrowly yellow, thence to margin sooty or brownish gray, with fringes concolorous. In many examples the yellow areas are greatly restricted, the dark bands being indicated by their darker richer tone on sooty ground; of the clear yellow areas of the paler forms, the basal portion, and the broad band between the transverse anterior and the median lines are the most persistent, and in many examples no other yellow remains; in the extreme forms, all the yellow disappears form the wings and the dark velvety transverse anterior and the median band are but faintly visible on the sooty ground, the yellow of the thorax being similarly obscured.

In the pale forms, the secondaries are light at the base, with a broad gray median band, a fainter and diffuse gray band in line with the transverse posterior of primaries, thence to the margin deepening gray with the fringes slightly lighter than the margin; in the dark forms, the secondaries are sooty, unmarked, the fringes concolorous. On both wings the vestiture is mealy land loosely attached, but with a satiny luster and a purple reflection.

The under surface of both wings has the basal portion, and the costa of primaries, yellowish in the paler forms, with the median line well marked, black or nearly so on its inner edge on primaries, accentuated on the veins on the secondaries and beyond this to the margin gray, the transverse posterior line also being present on this darker ground; in the dark forms, the wings beneath may be almost uniformly sooty black, unmarked, only slightly paler at the base.

Abdomen—﻿extending well beyond the secondaries; of almost uniform diameter, untufted; the vestiture much shorter and smoother than that of the thorax; in the pale forms, slightly more gray than the posterior half of the thorax; in the dark forms, sooty and concolorous with the secondaries.

Male genitalia—﻿of extremely simple type; the uncus simple, curved, evenly tapered; the valves densely hairy and almost without armature, except weak marginal spine-like hairs; a peaked clavus , and a fold arising from the sacculus , but these often scarcely distinguishable; the sacccus long and tongue shaped.

Of the pale and dark forms, the extremes seem to be seasonal in their appearance; the summer broods average paler in color, lighter in their markings, and smaller in size, than the spring brood from hibernated larvae; but these differences are not so uniformly apparent that it is always possible to determine, by the appearance of a specimen, from which brood it came.


"Ridingsii passes the winter in the larval stage in a carefully constructed hibernaculum. These hibernating larvae occupy sealed chambers low down in the dry stems of the leaves of flava, much more rarely in minor. This chamber is constructed in the dry corky frass which fills the lower portion of the leaf in which the larva has been feeding, is ceiled with an arched button of closely compressed particles line beneath with silk, the leaf forming the walls and another accumulation of packed frass the floor. The space occupied by the larva is usually about an inch in length, but is sometimes much longer. This portion of the leaf, dry and dead in flava, green in minor, shows no trace of feeding, though the larvae become active long before leaving their winter quarters.

About April 15th, they leave these hibernacula, rupturing the ceiled roofs and creeping up through the loose frass above. After an interval of several days spent apparently without feeding, during which they may be found in the litter of dead and broken leaves of the preceding year, they creep up the tender hew leaves, eat a round hole in the side, and immediately creep in. This occupies only about two minutes, and is the method of entrance without regard to whether the leaf chosen is a mature one, open at the top, or an unopened one. In the former case the larva ceils the open top with a transparent but strong silken web, and sometimes, but rather exceptionally, cuts a groove around the leaf internally, which eventually aids in bringing about the collapse of the upper portion of the leaf. This year, however, fully ninety five percent of the larvae chose immature, unopened leaves, the earlier leaves having been killed by the late frost.

In these closed leaves the larvae invariably commence feeding at the top of the leaf, soon causing the hood and closed lips of the leaf to collapse, thus effectually closing the tube and obviating the necessity for a ceiling web, which however, is sometimes spun some distance down the tube. The notch-cutting habit was not practiced in any of these immature leaves. As the larvae spin a carpet of silk wherever they go, this also aids in keeping the tube effectually sealed and in preventing the opening of the growing leaf. These hibernating larvae vary greatly in size, and molt at least once before the last larval stage is reached. After taking possession of a leaf, the lower portion of the tube fills up with corky frass particles, in which the cocoon is spun, the larva having previously cut two holes through the leaf wall, a large one above for the emergence of the moth, and by burrowing down in the frass-filled tube, a small one some distance below the location chosen for the cocoon, this second hole being apparently for drainage; just above this drainage hole and between it and the cocoon, the tube is sealed with a lightly spun web, usually not two closely spun to retain the water. The small hole where the larva entered the leaf, unless obliterated by feeding of plugged with the accumulated frass, is usually closed with a web. The larva sometimes changes from the old leaf to a new one, and when this occurs just before pupation, unlike semicrocea, it eats enough of the new leaf to furnish frass and nibbled particles to render the cocoon opaque; usually, however, the cocoon is composed of the corky frass particles loosely held together with silk, and is built against one side of the tube, the leaf-wall on that side forming one wall of the cocoon.

...In ridingsii the pupal stage lasts ten to twelve days, emergence taking place in the daytime, usually between twelve and four o'clock. The pupa sometimes forces itself through itself through the top of the escape of the moth. Pupation of the spring brood takes place from May 8th to May 20th, and the emergence of moths is complete by June 1st . The moths are extremely variable, some examples being suffused with black to the obliteration of all markings on the wings.

... Ridingsii is peculiarly free from parasites. Of several hundred larvae and pupae, only two were observed to be parasitized, and these by a tachina fly determined by Prof. C. W. Johnson to be Hypostena variablis Coq. The pupae have an active enemy in a bird (?) which systematically selects the leaves showing the large emergence hole and splits them down until the cocoon is reached, abstracting the pupa. In one field, perhaps a quarter of the entire brood was so destroyed."


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Source URL (retrieved on 2018-10-24 02:05): https://harvardforest.fas.harvard.edu/exyra-ridingsii