Barbara Robinson

By Dawn's Early Light: Matutinal Mating and Sex Attractants in a Neotropical Mantid

Females of the neotropical mantis Acanthops falcata adopt a special posture at dawn which is maintained for about 20 minutes. During the same period, males fly strongly, even in the absence of females. Our studies show that in this posture females are secreting a pheromone that acts as a sex attractant. All sexual activity in this species normally occurs between dawn and sunrise. It can be triggered by any dark-to-light transition, irrespective of real time. This sexual periodicity is probably an antipredator adaptation.

The structure, possible function and origin of the remarkable ladder-web built by a New Guinea orb-web spider (Araneae: Araneidae)

Summary The remarkable, perpendicularly-elongate web of a New Guinea araneid spider is described and illustrated. Its siting and construction are described and the possible origins and functions of the structure are discussed.

The Predatory Behavior of the Ogre-Faced Spider Dinopis longipes F. Cambridge (Araneae: Dinopidae)

Spiders belonging to the family Dinopidae catch their prey in small rectangular nets of hackled silk held at the corners by the first two pairs of legs while the net and the spider are supported by a scaffolding of silk. Dinopis longipes F. Cambridge employs the net to catch prey animals moving on a nearby substrate by thrusting the net against them. This form of prey capture has not been described for other species of dinopids and is described in detail and illustrated. Once the prey has been picked off the substrate, attached to the net, it is wrapped in silk and then bitten. Experiments showing that the predatory lunge can be elicited by purely visual stimuli are reported here for the first time. The predatory behavior of D. longipes is compared with that reported for other species and the differences are assessed in terms of adaptive function.

Adaptive Complexity: The Thermoregulatory Postures of the Golden-web Spider, Nephila clavipes, at Low Latitudes

The golden-web spider, Nephila clavipes (L.), responds to insolation from a wide range of compass bearings and altitudes by making postural adjustments that minimize the surface area of the body exposed to the heat source. The thermoregulatory postures involve pointing the apex of the abdomen at the sun and aligning the long axis of the body parallel to the suns direction. Experimental and observational studies show that the spider can adjust its position in response to dorsal, ventral (through the web) and lateral solar illumination, and to complex combinations of these types of illumination. It is thus able to effect reduction of insolation irrespective of the compass orientation of the web. Full descriptions of the range of postures are given along with an analysis of actual web bearings. Web orientation is primarily determined by the requirements of efficient prey capture and the availability of web supports. Thermoregulation by postural adjustment may be particularly complex at low latitudes because of the potentially high heating effect of the sun over the greater part of its daily transit. Many arthropods that are exposed to insolation at fixed sites (e.g., some web-building spiders, other sedentary raptors and cryptic animals that rest by day on a matching background) can be expected to possess complex behavioral adaptations related to thermoregulation.

Culture techniques for Acanthops falcata, a neotropical mantid suitable for biological studies (with notes on raising web building spiders

We think that we have found the solutions to these problems. We have devised a simple and inexpensive culture regime and found a species that is easy to manage in captivity. This species, Acanthops falcata Stol, is small enough to raise in large numbers in a modest amount of space and large enough to be convenient for a wide number of biological investigations. Females that are sexually receptive can be triggered to mate by a dark/light transition and males also become sexually active following such a transition. Matings are thus readily manipulable by the experimenter. In addition, the species is fecund and hardy. Our interest in solving the problems of raising predatory arthropods began in 1971, when we needed naive predators in order to investigate instinctive behavior. We used two species of araneid spiders, Argiope argentata and A. aemula, feeding them on dead drosophiloid flies (Robinson & Robinson, 1976a). Since then we have raised several generations of A. argentata and successfully hand reared two other species of web building spiders from egg cocoons, without the restriction of using dead prey, which makes the problem simpler.