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Tetragnathid spiders (Tetragnatha spp.) found in riparian habitats have recently been used as bioindicators of sediment contamination and insect-mediated contaminant flux. We investigated whether sexual dimorphism (size and behavior) influenced the female:male ratio in composite samples, stable isotope ratios (carbon [δ 13 C], nitrogen [δ 15 N]), and Hg concentrations in the southern United States. Additionally, we explored whether biomass for contaminant analysis could be preserved by using the legs of tetragnathids as a surrogate for whole-body δ 13 C and δ 15 N signatures. We found that female tetragnathids were significantly larger than male spiders and represented a larger proportion of spiders collected at all sites. However, despite the difference in size between sexes, no differences in growth dynamics, isotopic signatures (δ 13 C and δ 15 N), or mercury concentrations were observed. It was determined that the leg of a tetragnathid can accurately represent the stable isotope signature of an entire spider.

Urbanization poses serious extinction risks, yet some species thrive in urban environments. This may be due to a pronounced developmental plasticity in these taxa, since phenotypically, plastic organisms may better adjust to unpredictable urban food resources. We studied phenotypic plasticity in Nuctenea umbratica, a common European forest and urban vegetation spider. We subjected spiderlings to low (LF), medium (MF) and high (HF) food treatments and documented their growth and developmental trajectories into adulthood. Spiders from the three treatments had comparable numbers of instars and growth ratios, but differed in developmental periods. Longest developing LF spiders (♀ = 390, ♂ = 320 days) had the smallest adults, but MF (♀ = 300, ♂ = 240 days) and HF (♀ = 240, ♂ = 210 days) spiders reached comparable adult sizes through shorter development. While males and females had comparable instar numbers, females had longer development, higher growth ratios, adult sizes and mass; and while males adjusted their moulting to food availability, female moulting depended on specific mass, not food treatment. We discussed the patterns of Nuctenea sex-specific development and compared our results with published data on two other Holarctic urban colonizers (Larinioides sclopetarius, Zygiella x-notata) exhibiting high plasticity and fast generation turn-over. We conclude that despite relatively unconstrained developmental time in the laboratory enabling Nuctenea to achieve maximal mass and size-main female fitness proxies-their relatively fixed growth ratio and long generation turn-over may explain their lower success in urban environments.

Imidacloprid is a nicotine-based, systemic, widely used insecticide. In order to investigate the effects of imidacloprid on the spider Pardosa pseudoannulata (Araneae: Lycosidae), specimens were exposed to different concentrations of imidacloprid (12.5, 25, 50, 100, 200 mg/L) by the dipping method. Surviving spiders were used to determine the fecundity, development time of unexposed offspring, predation, and the activities of detoxification enzymes. Significant reductions were observed in survival rate and fecundity of spiders exposed to imidacloprid. The development times of unexposed offspring (F(1)) were prolonged significantly with increased concentrations of imidacloprid. Spiders exposed to concentrations of imidacloprid above 25 mg/L showed significantly weaker predation on Drosophila melanogaster than the control group, but a low dose of imidacloprid (12.5 mg/L) increased predation ability. The activities of carboxyl esterase, acetyl cholinesterase, and the mixed-function oxidase were significantly inhibited by imidacloprid. With increasing concentrations of imidacloprid, the activities of all three kinds of enzymes were decreased significantly. These results suggest that imidacloprid can stimulate the performance of spiders (in low concentration) and has chronic toxicity to the spiders.

Metal pollution is a serious environmental problem worldwide, and severely threatens biological diversity and human health. In order to investigate the effects of metals on a potential indicator species of wolf spider, Pardosa astrigera (Araneae: Lycosidae), 3rd-instar spiderlings were exposed to metals by using sublethal concentrations of PbCl₂ and ZnCl₂ solutions as their drinking water. The total durations of development of P. astrigera from the 3rd to 6th instars were significantly longer than that of the control group, and females showed a sharp reduction in total egg number. Body weights were significantly decreased in the mature spiders exposed to PbCl₂ solutions and ZnCl₂ solutions of high concentration (100 mM). These results suggest that detoxifying strategies deployed by P. astrigera against metal intoxication incur the costs of delayed development, and reduced growth and reproduction.

Most orb web spiders face downward on the web hub, and their webs are vertically asymmetrical, that is, the lower part of the web is larger than the upper part and the ratio of the lower part to the whole web area increases as the spider grows. This phenomenon may reflect biogenetic law such that young animals exhibit a general ancestral trait whereas adults exhibit specific and derived traits. An alternative explanation is that vertical asymmetry may arise from the difference in time required by spiders to move up or down the web to capture prey. The present study tested these two hypotheses for Eriophora sagana. Subadults of this species build their webs with reverse asymmetry in that the upper part of the web area is larger than the lower part. In both subadults and adults, the upper proportion decreased with spider weight, and adult spiders built more symmetric webs. These results support the capture time difference hypothesis.