The distribution, spatial clustering, and density of trapdoor spiders in two California coastal dune ecosystems

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  The distribution, spatial clustering, and density of trapdoor spiders in two California coastal dune ecosystems Abstract Coastal dune ecosystems support endemic trapdoor spiders, yet population data for these species are limited. We conducted the first coastal dune trapdoor spider population estimation surveys at Moss Landing State Beach (California) and for Aptostichus stephencolberti Bond 2008 at Sunset State Beach using randomly selected 1m 2 quadrats across ~26,000 m 2 per site. Burrow densities were similar between sites (Sunset: 0.287 burrows/m 2 ; Moss: 0.453 burrows/m 2 ), yielding estimated population sizes of ~35,206 and ~30,959 individuals, respectively. However, spatial analyses revealed contrasting patterns of burrow distribution. At Sunset State Beach, burrow presence was strongly associated with vegetation and occurred closer to plants, despite vegetation being randomly distributed. In contrast, no vegetation–burrow association was detected at Moss Landing, alth...

Parasitism of Leucauge tessellata (Araneae: Tetragnathidae) by a koinobiont polysphinctine wasp of the Acrodactyla genus-subgroup (Hymenoptera: Ichneumonidae)

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Parasitism of Leucauge tessellata (Araneae: Tetragnathidae) by a koinobiont polysphinctine wasp of the Acrodactyla genus-subgroup (Hymenoptera: Ichneumonidae)

Abstract

Polysphinctine wasps have evolved highly specialized life strategies that allow them to parasitize different spider hosts effectively. In this report, we document juvenile orchard orb-weavers Leucauge tessellata (Thorell, 1887) singly carrying larvae of a polysphinctine wasp from the Acrodactyla quadrisculpta-group. The wasp was identified using its morphological characteristics, mode of parasitism, and mt-COI phylogenetic analysis. Observations revealed that all three Acrodactyla sp. larvae collected were attached to the left mediolateral abdomen of the host spiders, where they consumed hemolymph until pupation. Before being killed by their parasitoids, host spiders exhibited modified web-building behavior, constructing a reduced cocoon web in place of the characteristic orb web of L. tessellata. Our PLS-PM analysis showed a significant negative correlation between the host spider's developmental stage and the parasitism rate (P = 0.02), which suggests that Acrodactyla sp. wasps selectively target juvenile L. tessellata, likely because they are less able to dislodge the larva from its attachment site compared to adult spiders. We speculate that the apparently consistent site of larval attachment in this specific spider-parasitoid interaction may represent a specific host-utilization adaptation in the observed Acrodactyla sp. wasps. Further investigation is warranted to strengthen evidence for our interpretation of this behavior and to explore its evolutionary implications.

Brian T. Sabanal, Yong-Chao Su "Parasitism of Leucauge tessellata (Araneae: Tetragnathidae) by a koinobiont polysphinctine wasp of the Acrodactyla genus-subgroup (Hymenoptera: Ichneumonidae)," The Journal of Arachnology, 53(3), 165-170, (2 January 2026) https://doi.org/10.1636/JoA-S-24-028