Homepage
Biology
Distribution
Classification
Conservation
Genetic Study
Literature
Links
How you can help
Picture Gallery
Contact Us
Is it a Dolomedes?
As adults, both European Dolomedes species are usually striking and distinctive in appearance. As well as being very large (adult females ca 18-23 mm and males ca 13-18mm body length), they are characterised by a white, cream or yellow stripe along the sides of both the carapace and abdomen which contrasts with the dark body (click here for a picture).
However, unbanded adults, which occur at a low frequency in D. plantarius populations, can be more difficult to distinguish from other species, as can both banded and unbanded juveniles. At all growth stages there is considerable variation in body colour and well as the colour and width of the stripe. Body and stripe colour may be the same or differ between the carapace and abdomen. Stripe width and boldness is very variable and some individuals also have paired white dots along the abdomen. Colour variation, particularly of the body, tends to be greater in D. fimbriatus than in D. plantarius and the stripe width also tends to be greater.
Despite all of this variation, the European Dolomedes have their own distinctive 'jizz'. Their size range, patterning and colour variation all overlap with those of other European spider species but their overall appearance remains distinctive at all growth stages. Their bodies are essentially cigar-shaped and powerful in appearance, tapering towards both ends. The legs and body are shortly hairy: when the spiders are under water, air trapped in the body hairs makes them appear silver.
The sexes are indistinguishable until they are subadult. In common with other spider species, as well as clubbed palps, the mature males have a broader, slightly shiny carapace, narrower abdomen and longer legs than the females. Their overall body length is several millimeters less than that of the females. Adult females are most conspicuous and unmistakable when they are carrying their bulky egg sacs: these vary in size from ca 8mm to ca 12mm and are held in the chelicerae and attached to the spinners. The abdomen is curled around the sac and so often only the carapce is visible (click here for a picture).
Species that cause confusion
The main source of confusion in the UK is with the semi-aquatic Pirata species, several of which have more or less distinct white lateral lines on the carapace. Mature Piratas are a similar size to Dolomedes of a third to a half of their adult size. Their 'jizz' is very different with a high and squared-off front to the carapace and rather bulbous abdomen. In the breeding season female Piratas are often seen carrying egg sacs but these are small (ca 5mm) and white and carried at the back, in the spinners (click here for a picture).
HOMEPAGE
This site is maintained by Helen Smith