New Zealand Entomologist 29: 99-102 (2006)
Short Communication Use of artificial cover objects for detecting red katipo, Latrodectus katipo Powell (Araneae: Theridiidae) Marieke Lettink1 and Brian H. Patrick2 1 2
University of Otago, P.O. Box 56, Dunedin, New Zealand. E-mail:
[email protected] Otago Museum, P.O. Box 6202, Dunedin, New Zealand.
Introduction Katipo are endemic widow spiders belonging to the genus Latrodectus (Theridiidae), a genus notorious for the dangerous bites of adult females. Latrodectus has a global distribution and is represented in New Zealand by two species; L. atritus Urquhart 1890 and L. katipo Powell 1871. Recently, it was recommended that these be referred to as ‘black’ and ‘red’ katipo, respectively (Patrick 2002). Both species of katipo have declined throughout their respective coastal duneland habitats and ranges. A recent nationwide survey for red katipo revealed they were present at only 46% of sites where they had been recorded previously (Patrick 2002). Threats to red katipo are degradation and loss of habitat due to historical and on-going processes, including replacement of the native sand-binder pingao (Desmoschoenus spiralis) with introduced marram grass (Ammophila arenaria), deliberate and accidental spread of exotic species such as Monterey pine (Pinus radiata), and damage caused by stock and recreational vehicles (Griffiths 2001). Although red katipo appear to have declined in number and distribution, the scarcity of detailed historical records and lack of a nationallyimplemented standard survey methodology mean that current rates of population declines and range reductions are difficult to determine. Monitoring is sporadic and consists of repeated sampling of some known populations over time in combination with surveys at sites were red katipo are scarce and/or have been recorded previously. Such surveys rely on hand-searching of suitable habitat, ideally by experienced observers. The probability of detecting katipo may vary according to the complexity and structure of the habitat being searched (Patrick 2002), observer experience, time-of-year, and the developmental stage, with spiderlings and males being more difficult to detect than adult females
(Troup 2004). This variability can remain despite efforts to standardise survey conditions in-so-far as this is possible. For instance, two successive 30 min searches conducted by experienced observers at the exact same site yielded 33 and seven red katipo, respectively (Patrick 2002). Collectively, these difficulties highlight the need for practical and robust monitoring methods.
Fig. 1: Lizard pitfall trap with plywood lid in
coastal duneland on Kaitorete Spit, Canterbury (left). Immature female red katipo Latrodectus katipo underneath a plywood lid (right). Katipo were typically found adjacent to spacers, often with associated snares and retreats.
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Red katipo have their last South Island stronghold on Kaitorete Spit in Canterbury. This site contains the most significant coastal sand dune system in New Zealand, both in terms of its size and condition, and its diversity of invertebrates (Patrick 1994). Although native plants such as the sprawling broom (Carmichaelia appressa) and pingao are the natural sites for red katipo snares and retreats, previous surveys have noted a tendency for red katipo to utilise human debris such as metal objects for shelter and construction of their snares (Patrick 1994, 2002). A predilection for rusty tins was noted by Forster & Forster (1973), who deliberately targeted these items when wanting to find katipo quickly. We report here on the coincidental use by red katipo of two types of artificial cover objects intended for lizards in coastal duneland on Kaitorete Spit.
Materials and Methods From November 2003 until March 2004, 600 lizard pitfall traps (4.5 L square white plastic containers (‘space-savers’ manufactured by Containment Solutions, Christchurch) were regularly monitored as part of a mark-recapture study of lizards on Kaitorete Spit. During this time red katipo of all developmental stages (particularly spiderlings) were commonly found under the plywood lids covering the pitfall traps (Fig. 1). Catching-webs, retreats and egg-sacs were also encountered. The plywood lids were designed to allow lizard access to pitfall traps while preventing their desiccation and predation. Lids were constructed of 12 mm treated plywood and supported above the pitfall traps by small ‘spacers’ (plywood squares 12 mm (H) x 20 mm (W) x 20 mm (D)) glued under each corner. Lids were secured using galvanised steel pegs. In October 2004, Onduline (http://www. onduline.co.nz) covers were installed at eight sites (32 covers per site), and checked monthly for lizards and red katipo from December 2004 until March 2005. Onduline is an extremely tough lightweight corrugated roofing and cladding product made from organic fibres saturated with bitumen. Previous research conducted at the eastern end of Kaitorete Spit near Birdlings Flat showed that lizards, particularly the gecko Hoplodactylus aff. maculatus ‘Canterbury’ (Hitchmough 1997, 2002) used these covers as diurnal retreats (M. Lettink unpublished data). There were two variations on the Onduline cover design: 1) single sheet 580 mm x 400 mm; and 2) double-layered stack made of 290 mm x 400 mm sheets. The two layers were separated by a small gap, created by short lengths (~20 mm) of circular pine dowel (10 mm diameter) that were glued under the centre and corners of the top sheet. Sheets were weighed down with small rocks and checked for katipo by sequentially overturning each layer (Fig. 2).
Results and Discussion Fig. 2: Lifting of double-layered Onduline cover
to check for lizards and katipo (left). A Canterbury gecko (Hoplodactylus aff. maculatus ‘Canterbury’) is revealed under the top sheet (right).
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A check of all plywood lids (n = 600) in April 2004 and again in May 2004 revealed 95 and 86 spiders, respectively. This represents a sampling ‘efficiency’ of 0.16 (April) and 0.14 (May) katipo/ cover/check. Checks of Onduline covers (n = 1024: 32 covers x 8 sites x 4 checks) produced
Detecting katipo with artificial covers
593 sightings of katipo. Individual katipo could not be distinguished, so sightings are likely to have included multiple observations of the same individuals. Onduline covers attracted more katipo than plywood lids, with 0.58 katipo observed/ cover/check. Almost half of all katipo observations (47%) were of adult females (n = 279). Occupancy of Onduline covers increased over time: 11% of katipo observations were made in the first month (December) compared with 33% in the fourth and final month (March). Mature females used the covers for breeding, with 234 egg-sacs sighted (including multiple observations of the same egg-sacs in different months). Two recently burst egg-sacs with 17 and 18 emergent spiderlings in close proximity were witnessed on one occasion (9 January 2005). Many sheets contained mature females with between one and five egg-sacs each. Females appeared to tolerate each other’s presence as many sheets held multiple females, although the corrugated nature of the material may have prevented females from seeing others. A male katipo on egg-sacs displaying guarding behaviour typical of females was also observed. For doublelayered Onduline covers, it was not unusual to find one or more geckos under the first sheet and katipo under the second sheet. Lastly, the remnants of a neonate McCann’s skink (Oligosoma maccanni) were found in the catching web of an adult female katipo. Although lizards on Kaitorete Spit are known to include spiders in their diet (Freeman 1997) the reverse has to our knowledge not been recorded. In summary, artificial cover objects appear to be an effective survey tool for detecting the presence of red katipo. Similar techniques have been successfully applied in invertebrate monitoring programmes in New Zealand (e.g., Trewick & Morgan-Richards 2000, Bowie & Frampton 2004). Onduline covers are cheap (~NZ$1 for a 290 mm x 400 mm sheet), easy to construct and distribute, and quick to check. Observer bias due to inexperience is minimal and all development stages are easily detected. However, their indiscriminate use for long-term monitoring (e.g., measuring changes in abundance over time) may be inappropriate as occupancy of covers may not necessarily reflect true abundance. For instance, occupancy timelags and comparatively greater occupancy were observed at sites where natural cover (primarily
pingao) was lacking. Hand-searching should therefore continue to be used where abundance and population trends are the desired monitoring objectives. Further research is needed to calibrate abundance estimates from cover objects placed in habitats of differing complexities against those obtained using hand-searches at the same sites. Following surveys, covers should be removed postbreeding to minimise effects on katipo populations. Careful selection of survey sites may be required to avoid anthropogenic disturbance - including offroad vehicle use - where this is a potential issue.
Acknowledgements We wish to thank the University of Otago and Department of Conservation (DOC) for financial support. Phil Sirvid (Te Papa Museum) and Grace Hall (Landcare Research) provided comments that improved this manuscript. This study was an unplanned but enjoyable part of DOC Investigation No. 3666. DOC staff, Jonathan More and volunteers provided field assistance. Colin O’Donnell and Brenda Green provided photographs. We thank Nga Pakihi Whakatekateka o Waitaha for their tautoko.
References Bowie MH, Frampton CM. 2004. A practical technique for non-destructive monitoring of soil surface invertebrates for ecological restoration programmes. Ecological Management and Restoration 5: 34-42. Forster RR, Forster LM. 1973. New Zealand Spiders – an Introduction. Collins, Auckland. 210 pp. Freeman AB. 1997. Comparative ecology of two Oligosoma skinks in coastal Canterbury: a contrast with Central Otago. New Zealand Journal of Ecology 21: 153-160. Griffiths JW. 2001. Web site characteristics, dis persal and species status of New Zealand’s katipo spiders, Latrodectus katipo and L. atritus. PhD thesis. Lincoln University, Christchurch, N.Z. Hitchmough RA. 1997. A systematic review of the New Zealand Gekkonidae. PhD thesis, Victoria University of Wellington, N.Z. Hitchmough RA. (Compiler) 2002. New Zealand threat classification system lists – 2002. Threatened Species Occasional Publication
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23. Department of Conservation, Wellington, N.Z. 210 pp. Patrick BH. 1994. Lepidoptera of Kaitorete Spit, Canterbury. New Zealand Entomologist 17: 52-63. Patrick BH. 2002. Conservation status of the New Zealand red katipo spider (Latrodectus katipo Powell, 1871). Science for Conservation 194, Department of Conservation, Wellington, N.Z. 33 pp. Trewick SA, Morgan-Richards M. 2000. Artificial weta roosts: a technique for ecological study and monitoring of tree weta (Hemideina) and other invertebrates. New Zealand Journal of Ecology 24: 201-208. Troup C. 2004. Katipo monitoring programme – Kaitorete Spit (Canterbury Conservancy). Unpublished report, Department of Conservation, Christchurch, N.Z.
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