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, temperature 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 distribution 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 predators) and indirectly (due to the impact of temperature and vegetation on the amphibian population, the leeches' major prey). Leeches of <1 g were found mostly in April and May following hatching, while those >5 g were predominant in September © Inter-Research 2011.