Skalistes inopinata (Burr 1900)

Skalistes inopinata (Burr)

During the day, this species was found in forks of large branches, on trunks of trees up to 5 m above the ground, and in a house; at night it was found on rotting Anona sp. fruit and on rotten wood.

Male cerci differ from those of females and nymphs in being longer and more crescent-shape. In addition, they have a horn-like triangular process that projects dorsally near the base (Figure 13). Male cerci have only a few teeth on the inner margin near the base (Figure 13).

We taped 7 high-level and 8 lower-level aggressive interactions. High-intensity aggression involved pinching. Most pinches were unilateral; in only 2 of 18 pinches did males seize each other simultaneously. Unilateral pinches usually were short in duration, lasting an average of 7.9±19.5 s (N = 17, median = 0.7, range = 0.1–71.1). The pinching male usually released the other spontaneously rather than being forced to do so.

Some pinches were on the cerci or at the posterior tip of the opponent's abdomen, and they were released relatively quickly. In six cases, the opponent was seized farther forward, with the distal, tong-like portion of the cerci (Figure 14). The pinching animal almost immediately twisted his abdomen so as to lift the opponent off the substrate and turn him upside down (Figure 14-3). Sometimes the pinching male then turned him back so the other male was right-side up again; in other cases the second male struggled and twisted to bring his tarsi back into contact with the substrate. In one mutual pinch one male was turned upside down, but he regained his footing, twisted his own abdomen, and turned the first male upside down twice in succession.

In general, forceful movements, such as strikes and slams, were relatively rare in this species as compared, for example, with Doru taeniatum, or with Carcinophora spp. and Vostox quadripunctatus (below). In some cases, however, one male swung his abdomen vigorously in an apparent attempt to slam against the other. In most of these swings (17 of 29), the male's abdomen was twisted so that the dorsal surfaces of his cerci (including the triangular processes) would hit the opponent; in nine other cases the male hit his opponent with the ventral surfaces of his cerci. It was not always easy to distinguish between vigorous tapping and weak slamming movements, especially because some apparent “slams” ended just as they reached the site where the other animal was, or had been when the slam was initiated. Some males made one or more apparent slamming movements while pinching the other male; in six of seven such cases the slams were directed dorsally. The quickest, most energetic movements were withdrawals from contact and twisting movements of the abdomen during pinches.

Lower-level aggression was much more common and included presentations in which the abdomen was bent forward and also twisted 90° so that one cercus was above the other, and the dorsal triangular structures were on the side closest to the opponent (or at least where the opponent had been when the maneuver began) (106 cases). Sometimes the aggressor's cerci touched the opponent on the abdomen or cerci (Figure 14), and sometimes they were held immobile in this position. More often (71%) the posterior end of the abdomen was swung in an apparently exploratory fashion, especially in a dorsoventral direction (which, because of the abdomen's turned and twisted position, gave the cerci an anteroposterior movement). Other presentations involved touching the opponent one or more times with the dorsal surfaces of the cerci. Usually swinging movements were relatively slow and short, and the quickest movements were short withdrawals when the cerci had made brief contact with the opponent. This pattern of movement reinforces the impression that the swings generally had an exploratory function.

A puzzling behavior seen in several pairs of males was apparent homosexual courtship (behavior indistinguishable from courtship directed toward females; see below) and repeated copulation attempts. In some cases, the male being “courted” responded aggressively, presenting and tapping as described above, or even pinching. The “courting” male usually continued his courtship unless the aggressive response of the other became forceful. In other cases, the courted male responded by twisting the tip of his abdomen 90° as would a receptive female, and the two males spent extended periods (up to 50 s) actively rubbing their genital areas against each other as if attempting intromission. On at least 14 occasions, it was clear, when males pulled apart momentarily, that one had at least partially everted his genitalia (Figure 15). In some cases, both males everted their genitalia during such interactions. Four apparent homosexual copulation attempts either immediately preceded or followed aggressive movements, such as presentation or a soft slam, by the same male (behavior patterns never seen in males courting females), so it was not clear whether homosexual courting represents cases of mistaken identity or fighting behavior in which primary male genitalia are used (an unusual if not unique phenomenon; Eberhard, 1985).

Another common, slightly lower-level aggressive behavior was to run toward the opponent, often hitting him one or more times (if he fled) with the head (especially the mouthparts). Such running attacks, which were unusual in that the abdomen was not bent farther toward the opponent than it was at the start of the attack, were seen 31 times. This type of interaction sometimes was associated with touching the other repeatedly with the mouthparts (“mouthing”), which occurred on 17 occasions. Usually the mouthparts contacted the cerci and/or posterior portion of the other male's abdomen.

Skalistes inopinata

We taped five courtships and one copulation. Courting males performed gentle forward-backward vibrations of the abdomen. They also tapped the female's head, thorax, and abdomen repeatedly with their cerci, mostly with the ventral surfaces of the basal or middle portions of the cerci. The male tapped with both cerci at once, sometimes by rocking his body backward, sometimes by moving his cerci ventrally, or a combination of the two. Sometimes the male tilted his abdomen from side to side as he tapped. At no time did the dorsal “horns” at the bases of the male's cerci touch the female. Acceptance was signaled when the female raised and twisted her abdomen slightly, and the male twisted and inserted his abdomen ventral to hers to copulate (Figures 77, 78).

During copulation the male sometimes gave single, brief dorsal flicks or jerks of his abdomen lasting only about 0.03 s (Figure 77), perhaps in response to movements by the female. In most cases, it seemed that his movement did not result in a new contact with the female, rather it pulled and/or twisted the genital union. Early in one copulation the male made eight flicks in the space of 50 s. Males also tapped and rubbed females gently with the bases of their cerci during copulation (Figure 78).

Two copulations were preceded by almost no courtship other than the male raising his abdomen and attempting to keep its tip directly toward the female. In one pair, the female repeatedly pursued the male, antennating him several times and bringing her abdomen around to press its ventral surface against that of the male's until the male successfully achieved intromission.