外来種クロガケジグモの鳥取市における分布拡大と在来種への影響

クロガケジグモ（クモ目ウシオグモ科）は鳥取市では2006 年に初めて生息が確認されたオーストラリア原産の外来性のクモで，2009 年におこなわれた分布調査では鳥取市の賀露から湖山近辺を中心に差し渡し最長で5 km ほどの地域に分布域が広がっていることが確認されている。2014 年に鳥取市内の主要な道路沿いで本種の分布を調べ，本種の分布が周囲の各方向に，平均してさらに3.6 キロメートルほど拡大していることを確認した。本種が生息しているところと未生息の地点で在来種のクモの個体数を比較したところ，本種がいるところでは在来種の個体数が著しく減少していること，また，本種の個体数と同地点に生息する在来種のクモの個体数は反比例することがわかった。クロガケジグモが好んで巣をつくるガードフェンスのパイプの隙間のような場所は，在来性のクモにとっても隠れ家や越冬場所として重要な生息場所なので，在来種はクロガケジグモによって生息場所を奪われていると考えられる。 / The Australian Black House Spider or Window spider, Badumna insignis (L. Koch 1872) (Desidae) is an introduced spider in Japan, which was first found in Osaka in 1963. In Tottori City (Tottori Prefecture), which is located about 150 km northwest of Osaka, the species was first found in 2006 at Koyama and its neighborhood (Fuse and Katsurami). The range of the species in Tottori Prefecture was surveyed rather extensively in 2008-2009 and it was confirmed that the spider is distributed only in a small area around Koyama with a maximum diameter about 5 km in Tottori City, with the exception of the second range expanding rather widely in Kurayoshi City and vicinities. We surveyed the range of B. insignis in Tottori City also in 2014 by checking and counting number of spiders found on roadside pipe guard fences per a section 10 m long (with additional data obtained in a preliminary survey in 2012) and confirmed that the range expanded ca. 3.5 km on average outward from 2009. We also confirmed that the number of individuals of native spider species on pipe guard fences was significantly low at sites where B. insignis was found sympatrically. It seems that B. insignis has deprived of habitats and overwintering sites from native spider species by occupying empty spaces inside pipes which open at the joints of poles and guard rail pipes of the pipe guard fence in order to make their webs.