Gerris thoracicus

Gerris thoracicus is a widely distributed water skater of ponds and lakes with a preference for organically enriched, slightly polluted or saline conditions. It tolerates a higher salinity than other British gerrids. Eggs are laid on the floating leaves of aquatic plants in April and May, which give rise to a first generation of adults by mid summer. These produce a second generation, the adults of which overwinter. G. thoracicus is usually fully winged and able to fly.

Gerris-thoracicus-with-map

The map is based on records from NBN Gateway, with yellow dots showing pre 1990 records, reds dots 1990 – 2015 records and red on yellow dots overlapping records. A widespread species in the UK, which also occurs throughout Ireland.

Gerris thoracicus is 10 – 12 mm in length and the commonest of the three species of Gerridae that have a yellow-brown disc on the pronotum, a feature more obvious in dry specimens.  The other two species are G. costai (which is larger) and G. lateralis (which has patches of silver hairs along each side of the ventral surface of the abdomen).