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Water spiders (Dolomedes)

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Taxonomic group

Pisauridae: Dolomedes

Diagnostic features

Dolomedes is a genus of spiders that includes species capable of entering the water. They are quite large, reaching up to 75mm in leg span. Dolomedes are known as “nursery web” spiders due to their nests made of dense blankets of web often seen on the outer branches of bushes.

[Dolomedes]. Image: Stephen Moore Image
Dolomedes. Image: Stephen Moore
[Dolomedes]. Image: Stephen Moore Image
Dolomedes. Image: Stephen Moore

Typical habitats

Dolomedes can be common along the stony or weedy margins of streams and rivers. They are usually seen above the water, but they can retreat into the water by climbing down emergent vegetation.

Feeding

They are predators of invertebrates (possibly also small fish), and have been seen catching stream insects as they emerge from the water.

Indicator value

  • Hard bottom: 5
  • Soft bottom: 6.2

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

Dolomedes are found along farmland and urban streams, and since they live primarily above the water they may not be very sensitive to water quality. They have been assigned tolerance values of 5 (hard bottom sites) and 6.2 (soft bottom sites).