Seasonal variation in the occurrence of the medicinal leech Hirudo orientalis in Guilan Province, Iran

Abstract

Two small populations of medicinal leeches Hirudo orientalis Utevsky & Trontelj, 2005 were sampled monthly over the course of a year (November 2008 to October 2009) in 2 separate regions of Guilan Province in northern Iran. Environmental factors, including host availability, tem- perature and vegetation density (biomass in g km -2 ) were analyzed to assess their impact on leech populations. The study areas supported only low densities (ind. km -2 ) of medicinal leeches, mostly due to agricultural activity which has caused habitat destruction and has gradually limited the distri- bution of leeches to small, patchy bodies of water. Agricultural activity is seasonal, so leeches are not affected by this activity equally year round. Leeches were most abundant in May/June, were present in small numbers in July/August, and hibernated from December to March 2009 at both sites. Leech density was significantly correlated with amphibian density (biomass in g km -2 ), the major hosts in the sample areas. Temperature and aquatic vegetation densities affected leech numbers directly (temperature influencing leech growth rate and vegetation providing shelter from potential preda- tors) and indirectly (due to the impact of temperature and vegetation on the amphibian population, the leeches' major prey). Leeches of 5 g were predominant in September.