Fishing Spider - Dolomedes sp. A (undescribed)

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Fishing Spider - Dolomedes sp. A (undescribed)

I discovered this handsome fishing spider under an exposed rock in the middle of a small creek. The rock (a piece of limestone) was resting on a couple of other limestone rocks with water continually running over them, after rain all rocks would probably be submerged. The spider had a small web-lined retreat and likely remained there during floods and as can be seen by its very hairy state, would trap air around its body to enable it to breathe underwater.

This is the only individual of this species encountered, but as the creek has many areas of exposed limestone, it would probably be found elsewhere along the waterway. The body length was a little over 2 cm (nearly 1") with a total span of around 8 cm (over 3"). Such water spiders can not only walk on water, but swim under it too, where they hunt small fish, tadpoles and aquatic invertebrates.

There is another fishing spider in the area (that I shall detail next), which is more common, less hairy and can also be found well away from water. Apparently this other species is the only Dolomedes recorded for WA. The Giant Water Spider, Megadolomedes australianus is also found in WA, but this species although larger has much longer/finer legs and is also less hairy (I have not encountered this species in the Esperance region).

Fishing Spider - Dolomedes stilatus

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Fishing Spider - Dolomedes stilatus

A widespread spider of well watered areas around Esperance and although a Fishing Spider, it will happily take to surrounding areas when ephemeral swamps dry out over summer. I had one that bred in my external laundry during January after all surrounding surface water had disappeared. She produced dozens of offspring that climbed to the roof and presumably ballooned away.

As the photographed spider is reasonably common, I have used the name Dolomedes stilatus as it is currently the only Dolomedes species listed for WA. The body length is around 2 cm (1") and the total span around 8 cm (over 3"). It is attractively marked with two bright orange stripes along the cephalothorax making it quite distinctive, so is unlikely to be confused with other spiders.

This fishing spider is active in, on and around small lakes, swamps and ponds where it hunts aquatic animals including small vertebrates like tadpoles and fish, but will also take land-based invertebrates. These spiders are also known as Nursery-web Spiders as the surrounds of the nest are clothed in silk strands, which the spiderlings use to get around and eventually to climb to a high position in order to balloon away. The mother is very attentive and will stay to extend the nursery-web strands and protect her young until they (en-mass) take their leave.

Nursery-web Spider - Pisauridae - probably Dolomedes

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Nursery-web Spider - Pisauridae - probably Dolomedes

A common spider in the district and usually found at night on the ground, or in low twiggy vegetation. Their eyes brightly reflect a torch beam and they can be easily detected by holding a torch to your eye and scanning at or near ground level. Although closely related to the fishing spiders, these tend not to be as large with body length usually less than 2 cm (3/4"), with a span of around 6-7 cm (less than 3").

The general appearance of these spiders is in many ways very similar to Wolf Spiders from the family Lycosidae. The main difference (without microscopic examination) is the eye arrangement and size. These spiders (Pisauridae) have two curved rows each of four eyes, with all being similar in diameter, or the top four slightly larger than the lower row. The Wolf Spiders on the other hand have three rows, the bottom row of four small eyes, then the row above with two large eyes, and above them (and further apart), another two smaller eyes.

Another obvious difference between these spiders is the female Nursery-web Spider carries her egg sack immediately below her body, whereas the female Wolf Spider drags the sac behind her. In one of the photos above the female is guarding her egg-sac below her.

These particular Nursery-web Spiders do not require the presence of water to survive and can be found on any night that is not too cold, windy or dry. These as with most nocturnal spiders are usually most active when it is warm, calm and humid.

I notice in Wikipedia that they have a list of Pisauridae genera and species that is claimed to be current 2008, of which they list three species (all Dolomedes) that are found Australia wide, which presumably includes the Esperance region. One is Dolomedes stilatus that I believe is the common Fishing Spider found here (see post), and the other two are Dolomedes facetus and D. mirificus. It is therefore likely that one of these species is the subject of this post, but unfortunately I do not have the taxonomic details to determine the situation.