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Immature Stages of Cyrtidae

First instar larvae of Cyrtidae are of the planidium type, and are able to undergo a free living period of considerable duration without food. Locomotion is either by a looping motion or by jumping. In the latter case, the larva of Pterodontia stands erect on the caudal disk, which is specialized for the obvious purpose of giving a firm hold on the substrate, and projects itself into space by the sudden downward thrust of the long caudal cerci, bringing them into line with the longitudinal axis of the body from a position at right angles with it (Clausen 1940/62). However, Bovey (1936) found this to be accomplished in O. pallipes by the lowering of the head to the substrate near the point of attachment of the caudal disk, thus forming almost a circle, following which the body was abruptly straightened. This action simulates that of a released spring. The planidia of Opsebius are able to crawl in a looping manner along a single strand of a spider web (Cole 1919). Jumping does not seem induced by the host presence, but it serves to accomplish dispersion. Actual host contact is mostly by chance, and the planidia, when alert and awaiting a host or stimulated by its presence in the immediate vicinity, assume an erect position (Clausen 1940/62).

It is not know exactly how long the planidia are able to life if contact with a host is not made. One weeks seems to be the maximum, which is short in comparison with that for planidium larvae of other groups of insects. The planidia enter the bodies of their hosts probably through the thin membranes of the articulations of the legs. While doing so they cause appreciable irritation to the host spiders, and Theridium adults bearing planidia of Opsebius scratched themselves excitedly, seemingly being able to kill some of the parasitoids with their mandibles (Cole 1919).

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Fig. 162

Fig. 163

King (1916) recorded finding the planidia of Pterodontia in all parts of the host body, even in the legs and palpi, although the majority were in the thorax. They persist in this stage, without much growth or direct relation to any host organ, until springtime. Millot (1938) found Ogcodes pallipes young larvae in the abdomen during winter, but they migrate to the respiratory organs in the early spring and the first molt follows. Part of the second stage is also passed in the abdomen, and the second molt occurs there. The larva of Astomella lindenii Er., while in the host abdomen, derives air from one of the lung chambers of the host by placing the caudal spiracles against the lung wall and seemingly making a minute perforation (Brauer 1869a). This also occurs in O. pallipes, although Millot (1938) found some individuals to perforate the abdominal wall instead and thereby make direct connection with the outside air. In the latter, there is evidence of the formation of a respiratory funnel which is comparable to many Tachinidae.

Third instar larvae complete their feeding quickly and consume the entire contents of the host abdomen. Emergence is through a hole cut in the ventral abdominal wall. The host spider usually shows no evidence of parasitism, either by modification in body form or a change in activities, until just a few hours before it dies. However, the spider does spin a mat of silk just before death, and Locket (1930) noted that this was done even by male spiders, which was abnormal. He attributed this action in both sexes to increased pressure within the abdomen from the large parasitoid body; a measure of relief is probably obtained by expelling the silk.

Pupation.-- Pupation is outside the host body, in either the web or the burrow or in some sheltered place near the place of host demise. Emerged larvae of Acrocera fasciata Wied. suspended themselves in the host web by clinging to a strand with their mandibles; they were supported also by strands beneath the body (Emerton 1890). A sticky body surface aids the mature larvae to retain their positions in the web or on a trunk. Actual pupation usually occurs the day following emergence from the host, and the meconium is cast by the prepupa. The pupal stage is short, being 7 days in Pterodontia, 6-11 days in O. pallipes, and about the same in several other species in summer. Adult emergence occurs through a median longitudinal break over the prothorax of the pupal shell. There seems to be only a single generation annually, 9 or more months being passed in the first larval stage within the active or hibernating spider.

The eggs of all species of Cyrtidae thus far described are of minute size, rarely exceeding 0.25 mm. in length, pear‑shaped in outline, and brown to dull black in color. Millot called attention to an adhesive disk at the larger, posterior end of the egg of O. pallipes (Fig. 162A) by means of which it becomes firmly attached to any object upon which it may be deposited.

The first‑instar larvae have been described for O. pallipes Bovey 1936; Millot 1938), Ogcodes sp. (gibbosus L. or zonatus Er.; Konig 1894), and P. flavipes. All are distinctly of the planidium type, are 0.3 to 0.4 mm. in length, and have heavily sclerotized segmental plates both dorsal1y and ventrally. In Pterodontia, the body is fusiform, whereas in others it is more elongated, approaching the vermiform. P. flavipes (Fig. 162D, E) is distinguished not only by the exceptiona11y long caudal setae, or stylets, nearly half the length of the body, which in other species do not exceed the length of the last abdominal segment, but by the palmate scales which occur in transverse rows upon the dorsum of the thorax and ventrally on all body segments except the first and last. In other described species, these scales are replaced by simple though heavy spines. 0. pallipes (Fig. 162B) and several others of that genus have two pairs of spines, rather than one, on the caudal segment.

The head is relatively small, and, in 0. pallipes, the mouth hook terminates in a sharp, upwardly curved point and the three pharyngeal plates are long and slender. The last abdominal segment of 0. pallipes (Fig. 162C) is highly developed as an attachment organ, consisting of the usual adhesive disk and, in addition, three strong hooks, of which the outer two are simple and the median one bifurcate. These structures apparently relate to the manner of jumping and serve to brace and hold the body more firmly than is possible with the disk alone.

There is a difference of opinion regarding the occurrence of an open respiratory system in the first‑instar larvae of this family. Konig stated that Ogcodes sp. bears a single pair of spiracles in two funnel‑shaped depressions at the posterior margin of a triangular "shield" on the penultimate abdominal segment. In 0. pallipes, they are situated dorsolaterally upon the anterior portion of the last segment. King, however, noted that spiracles are lacking in Pterodontia and that the two crescentic areas at the posterior margin of the eighth abdominal segment, which superficially resemble spiracular openings, are in reality only the notches in the dorsal plate in which the caudal cerci fit when the larva is in the erect position.

The second‑instar larva was not described for any species when Clausen (1940) published his book, though several authors had stated that it has a very close resemblance to the third instar.

The fully fed third‑instar larvae of Ogcodes costatus (Fig. 163) and P. flavipes are rather robust, rather indistinctly segmented, and widest in the mid‑abdominal region and have a marked constriction between the thorax and abdomen (Kaston 1937). The posterior portion of the abdomen tapers sharply, and the last segment is broadly conical. The integument is delicate and entirely unornamented except in 0. pallipes, which has two longitudinal bands of minute "granulations" along each side of the abdomen, and P. flavipes, which has pairs of pad‑like areas armed with crochets on the ventral surface of the 5th to 11th body segment. The mouthparts are small and relatively simple.

In 0. costatus and O. pallipes, spiracles are present on the first thoracic and the eighth abdominal segments only, whereas the anterior pair of Pterodontia is believed to be on the mesothorax. This pair of spiracles is apparently not functional in 0. pallipes and Pterodontia.

There is a marked similarity in form between the pupa of all species that have been studied. The variable characters noted are the crest, or groups of presumed sensory organs on the head, and the number of spiracles. The V‑shaped crest of Pterodontia consists of a large number of club‑shaped processes; in 0. costatus (Fig. 163) and 0. pallipes, they occur in two groups on each side of the head. Astomella lindenii lacks the crest, or groups of processes on the head, and has a row of spines on the dorsomeson of the thorax. Brauer recorded six pairs of abdominal spiracles in Astomella, several species are thought to have four pairs, and King mentioned three in Pterodontia. Millot found four functional pairs on the anterior abdominal segments of 0. pallipes, followed by two vestigial pairs on the next segments. He called attention to the occurrence of only four pairs of abdominal spiracles on the adults of this family and consequently consider it probable that the pupae will be found to have a like number.

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