DOI: 10.5061/dryad.1vhhmgqq1
title: New live capture Araneae trap for ecologically sensitive areas

description: Contemporary field sampling methods for collecting invertebrates are typically destructive posing a risk to invertebrate populations many of which are already threatened worldwide. As an important ecological keystone order with extensive links with other trophic levels, spiders (Araneae) can act as indicators of ecosystem function. We present a novel non-kill trap designed to sample ground dwelling Araneae. The Sanctum Aranearum is a trap baited with structural complexity; the internal structure of the trap is designed to maximise surfaces available for web. The trap is open by design so that animals are free to enter and exit in order to minimise bycatch fatalities. Sancta Aranearum were field tested over three months at two sites in two types of vegetation. Traps were emptied monthly and total within-trap fatalities were recorded alongside vertebrate bycatch. Total invertebrate fatalities were minimal with Araneae cannibalism only occurring in one Sancta. As part of this proof-of-concept, invertebrates were destructively sampled for identification and included a wide variety of genera from both the target group (Araneae) and bycatch groups including small bodied groups often missed by pitfall traps. The Sanctum Aranearum is functional as a non-kill alternative trap allowing repeated sampling in sensitive areas, such as Orokonui Ecosanctuary where it has been approved for use. The trap can be constructed with minimal cost so is suitable for educational activities. We encourage further testing of this new design.
description: The Sanctum Aranearum was built to encourage residence rather than completely trap the invertebrates, hence the use of the word Sanctum rather than trap. The outer casing consisted of a white plastic pail (180mm length x 180mm width x 190mm height); the white colouration allows exposed Sancta Aranearum to mitigate internal temperature built up in the field through reflectance (Shiukhy, Raeini-Sarjaz & Chalavi, 2015). The lid was retained and used on the pail to shield the internal Sanctum Aranearum structure from weather and prevent birds easily accessing any invertebrates inside. Two windows were cut near the top of the pail on each chassis wall to allow animals to enter and exit at will. The size of these windows can be customised depending on preferences; in our case the windows were 2cm high and 4cm wide due to the presence of the large spider Dolomedes minor (L. Koch, 1876) at the study sites. The casing was filled with sand to the level of the windows to create a near-seamless transition from outside to inside habitat. The sand also controls humidity levels within the Sanctum Aranearum, trapping moisture and slowly releasing it during drought periods to keep the inside humid once it equilibrates with the surrounding environment (Vriend, Arran, Louge, Hay & Valance, 2017). This also prevented flooding from intermittent rain. Twelve 50ml centrifuge tubes and twenty 2ml microcentrifuge tubes were used to emulate crevices in rocks and bark within the Sanctum Aranearum and were buried in the sand with only the apertures exposed to allow animal access. To further increase structural complexity within the Sanctum Aranearum, two 40cm lengths of wire were bent into varying arcing shapes and anchored into the sand at both ends to create a zone of wiring above the tube apertures (Figs 1, 2). The pilot study was conducted from October 7th (Southern Hemisphere spring) 2019 to February 2020 on two rural properties within 30km of Dunedin, South Island, New Zealand. On each property, areas of grass-dominated pasture and adjacent areas of regenerating native forest dominated by Kunzea robusta (Myrtaceae) were selected for trap placement. At the northern site, Waitati (lat 45.7466°S, long 170.5655°E, 40 m a.s.l.), the available pasture was 100m distant from the forest margin, however, at the southern site, Taieri (45.0221°S, 170.2296°E, 20m a.s.l.), the available pasture was immediately adjacent to the forest margin. Despite this difference in proximity, the pasture communities were structurally and compositionally similar between sites as were the two forest communities. Four Sancta Aranearum were placed in each vegetation type at each site giving a total sampling effort of 16 Sancta Aranearum. A minimum distance of ten metres was maintained between Sancta Aranearum to minimise risks of interference (Digweed, 1995) without compromising the similarity of vegetation being sampled. Sancta Aranearum were semi-buried so that the ground was level with the sand within the traps. All Sancta Aranearum were emptied monthly over the three-month sampling period and checked for vertebrate bycatch. For the purposes of this proof-of-concept, the invertebrate contents of each Sanctum Aranearum were harvested destructively by transferring directly to 70% ethanol. All invertebrates were identified to family level or as close as possible. Araneae were identified to species or as far as current literature allowed. In future projects involving the Sanctum Aranearum, invertebrates can be collected, photographed and then released back into the field site without unnecessary fatalities. For a few highly abundant and fast moving or small invertebrate taxa, numbers in the traps were capped at fifty when more than fifty individuals were clearly observed to minimise bias. For example, one Sanctum Aranearum sampled contained more than 200 individual amphipods when opened; the animals quickly scattered and only a fraction could be collected so an estimation of fifty individuals was used. This also applied to Sancta Aranearum when sampling maggots and springtails which could reach numbers well over 200 per trap, but were unlikely to have been fully sampled during collection. Fragmentary remains of invertebrates, including exuviae and prey remains, were recorded alongside living invertebrates. Prey remains and dead invertebrates were counted to contrast with living invertebrates observed.