Submerged oviposition behaviour in the Large Red Damselfly Pyrrhosoma nymphula (Sulzer) on the Isle of Lewis
by ALICE STARMORE
First published in the Journal of the British Dragonfly Society, September 2008
The Large Red Damselfly Pyrrhosoma nymphula was observed and photographed in oviposition at two locations on the Isle of Lewis in the summer of 2007. The usual method was for the male, with the female in tandem, to land on a stem of the Bogbean Menyanthes trifoliata and then, with both grasping the stem, the female to start laying eggs in the stem, progressing downwards until her abdomen was about half submerged, while always holding her wings clear of the surface. On one occasion a female grasped a leaf with the abdomen three quarters submerged and the wing tips immersed. On 1 July the female of a pair became completely submerged. In all cases the male remained in the sentinel position while contact guarding the female.
Contact guarding is normal in most coenagrionids (Corbet, 1999). Complete submergence of the female during oviposition is also the main, or even the exclusive, behaviour for certain members of this family (Corbet, 1999) including some species of Coenagrion (Sawchyn & Gillott, 1975) and Enallagma (Bick, 1972; Fincke,1986; Cham, 2008). In some species in other coenagrionid genera it may be facultative, e.g. Cercion (Naraoka, 1990) or infrequent, e.g. Chlorocypha (Miller, 1995) and Ischnura (Matsuki, 1969; Jurzitza, 1986; Fincke, 1987; Kano, 1989; Cordero, 1994). However, there appear to be no published records of the occurrence of complete submergence in Pyrrhosoma.
The depth to which submerged females descend varies with the species (Corbet, 1999). For example, Lestes sponsa only descends about 1cm (Itô & Eda, 1977), whereas Enallagma has been recorded descending to a depth of about 1 m (Macan, 1964). The duration of submergence is also variable and can often be between 30 min and 1 hour (Corbet, 1999), as in Enallagma (Doerksen, 1980; Miller, 1990a); Fincke (1986) reported an average submergence time of 18.4 minutes for Enallagma hageni.
The Large Red Damselfly Pyrrhosoma nymphula is a typical contact guarding coenagrionid and is one of the commoner and most widespread damselflies in Britain, extending from the south coast of England as far north as the Orkneys (Brooks, 1997). The following is an account of the location, conditions and the sequence of events during oviposition of this species.
The location was a small depression in the moorland, situated between a burn called Allt Raonadale (100 metres to the south) and Loch Gillevat (80 metres to the north). The depression lies 850 metres from the cliff top on the north-east coast of Lewis. The depression is roughly 1 metre lower in level than the surrounding moor and contains two bog pools surrounded by very damp Sphagnum lawn vegetation. The larger pool contains a good growth of Bogbean Menyanthes trifoliata - plenty to serve as useful perches for oviposition but not so dense as to completely obscure views. The surrounding low bank is considerably drier and the vegetation is mainly composed of heather Calluna vulgaris,woolly hair-moss Racomitrium lanuginosum and purple moor-grass Molinia caerulea. The low bank provides some shelter from the wind and, when conditions are good - which is not very often - it is an ideal location for observing the local Odonata.
I always take my telescope for more detailed observation and so that I can avoid trampling the margins of the pools, which are fragile. Indeed, all of the vegetation within the depression is delicate and I take care to walk on it as little as possible - barefoot if weather permits. In June and July I approach from the Allt Raonadale (south-west) side of the pools so as not to disturb the pair of Red-throated Divers and their chick on nearby Loch Gillevat. Photographs were taken of the Large Red Damselfly Pyrrhosoma nymphula during oviposition sequences. The camera used was a Sony Cyber-shot DSC–N2 which provided timing to the nearest second.
Table 1, Photograph 1, 10.32.01 BST