Relation between the outer cover of the egg case of Argiope aurantia (Araneae: Araneidae) and the emergence of its spiderlings

To emerge from the egg case, Argiope aurantia spiderlings must penetrate a tightly woven outer cover composed primarily of large-diameter cylindrical gland fibers and small-diameter fibers, likely of aciniform gland origin. They accomplish this using enzymatic digestion and mastication to form a communal hole in the outer cover. The involvement of proteolytic enzymes in this process was demonstrated by zymography of spiderling homogenates and washes made from the edges of holes. The specific source(s) of the proteases is unknown, but histological examination of spiderling sections indicates that the digestive tract, venom glands, and gnathocoxal glands are all functioning at the time of emergence from the egg case. Observations on edges of holes indicate that spiderlings are able to solubilize the small-diameter fibers completely, but cylindrical gland fibers only partially. In the outer cover, cylindrical fibers are composed of numerous fibrils embedded within a matrix. Spiderlings appear to be unable to solubilize the fibrils, but digestion of the matrix allows the spiderlings to push the fibrils aside to create the opening.     

Effects of Early Contact with Maternal Parent on Locomotor Activity and Exploratory Behavior in Spiderlings of Hogna carolinensis (Araneae: Lycosidae)

In this study we investigated the effect of rearing conditions (stimulus complexity) on the locomotor activity and exploratory behavior of spiderlings of Hogna carolinensis in a novel open field arena. Experimental groups consisted of spiderlings that were allowed to remain with their maternal parent for 1 day (group 1), 3 days (group 2), and 5 days (group 3) after emergence from their egg sacs, and those who had no contact (group 4) with a maternal parent. Spiderlings that had physical contact with their mothers for 3 and 5 days required significantly less time to enter the arena, to reach the central grid area of the arena, and for an initial return to the start box than spiderlings in groups 1 and 4. In addition, spiderlings in groups 2 and 3 exhibited a significantly greater number of grid crossings as compared to groups 1 and 4, and spent more time in the arena. This is the first demonstration that environmental complexity, in the form of a social factor such as physical contact with a maternal parent, can affect the subsequent behavior of spiderlings.     

Survival strategies of the crab spider Thomisus onustus Walckenaer 1806 (Chelicerata,Arachnida, Thomisidae)

Summary The initial energy supply of emerging spiderlings is relatively meagre, so survival without feeding on insects during a spell of bad weather is limited to a period of a few days or weeks. During our investigations, spiderlings of Thomisus onustus (Arachnida, Thomisidae) were kept on different diets. There was a significant difference in survival rate between spiderlings that were starved or fed on pollen, nectar, or Drosophila. The results showed that pollen and nectar can be a source of energy for spiders for an extensive period. This demonstrates another way in which spiders may survive starvation when insect prey is lacking and thus ensure the survival of a whole population.     

Spiderling sex ratio and maternal investment in the bolas spider Mastophora cornigera (Araneae,Araneidae)

Male Mastophora cornigera exit egg sacs as adults, which allowed us to determine spiderling sex ratios and patterns of maternal investment in this species. We collected 15 egg sacs produced by seven mothers, which yielded 1945 emergent spiderlings which were sexed, 1850 of which were weighed. Two emergent broods were significantly male and female biased and were unaffected by pre-emergence mortality. The weights of male and female spiderlings differed in eight broods, with males and females being heavier in four cases each. Five of these broods were derived from multiple egg sac sets produced by one mother, and in each case, the total mean male and female spiderling weights for all broods in a set were biased in the same direction as the biased brood(s) within that set. Mean emergent spiderling weight was independent of brood size and sex ratio for both males and females. Despite such independence, sex allocation in M. cornigera can favor sons, daughters, or both equally, and by numbers, by weight, or both at once. The proximate mechanisms and adaptive significance of such variability is unknown. We also review evidence for gender-biased allocations in arachnid offspring and suggested mechanisms for their applicability to M. cornigera.     

A Stochastic Model for the Predatory Behaviour of Naive Spiderlings (Araneas: Salticidae)

A stochastic model is proposed for the hunting behaviour of jumping spiders when they are newly emerged from the egg-sac. The model takes into account the fact that the spiders are often unsuccessful when they attempt to catch prey for the first time and also the fact that their rate of response to prey slows down with time if they are unsuccessful. It is shown that the spiderlings ability to catch perceived prey improves with the number of prey captured. The model has been fitted to experimental data using the method of maximum likelihood and a good fit has been obtained. The model could be used as part of a model for the whole predation system.