Olfaction and prey search in the carnivorous leech Haemopis marmorata

Haemopis marmorata, the green horse leech, is carnivorous and readily eats earthworms. Using a Y-maze with flowing water, we show that specimens of H. marmorata are attracted to live earthworms. Ablating the dorsal lip, the presumed site of the chemoreceptors that this species uses in prey search, disrupts the ability of the leeches to find the earthworms in the Y-maze. Earthworm wash, a preparation of the collagen coating of earthworm skin, shock-induced earthworm secretion, mammalian blood and a salt­arginine mixture are not attractive to the green horse leech. The tails of freshly killed earthworms are attractive to the leeches, but tails from worms killed 8­12 h previously and stored cold are not. Our conclusion is that the earthworms produce a metabolite that attracts the leeches.