Crab Spider - Sidymella sp.

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Crab Spider - Sidymella sp.

Sidymella (Crab Spiders) is a genus in the Thomisidae family, which it shares with the Flower Spiders (see here). These are quite small with the above male being 4-5 mm (little less than 1/4”) in head and body length, whilst the female is around 7-8 mm (little more than 1/4”), so not noticeable to casual observation. They are also well-camouflaged in habitat, with the above being found on sedges where not uncommon. 

There are 8 described species, but probably many more await discovery and description. They are distributed throughout Australia, but as they are small, well camouflaged, do not build a web and wait in ambush for long periods, are usually only encountered accidentally when forced to move. Typically with Crab Spiders, the rear pair of legs are very small in comparison with the front pair and permit the spider to move in any direction including sideways (like a crab). The front legs are openly extended to rapidly grab any passing prey, with the first pair being longer than the second. 

Spiders in the Sidymella genus have a triangular shaped abdomen that is truncated at the rear end; the cephalothorax (head end) is pear shaped with the widest portion adjacent to the abdomen. Despite the male and female couple above being found within a kilometre of each other (approx. 20 km or 12 miles east of Esperance), plus the markings appearing related, I have no other indication that they are the same species.

Flower Spider - Diaea species 'Mallee'

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Flower Spider - Diaea sp. 'Mallee'

Flower Spiders belong to the Thomisidae family along with 27 genera and nearly 150 Australian species, and this only represents the described ones, as many like the above await scientific classification. There are a number of white spiders in this group, but those in the genus Diaea can be recognised by the eye arrangement that is shaped like a smiley mouth.

These are ambush spiders that normally wait camouflaged on similar brightly colored flowers for a visiting flying insect in hope of a nectar meal, but end up being a meal themselves. Interestingly, the spiders above were not on a blooming flower - one was under a cluster of bright yellow pop-flowers, whilst the other was on a very odorous plant that had finished flowering, but clearly still attracting flying insects, as this spider was waiting exposed on top of a leaf and possibly hoping it looked like an actual flower, which may represent another hunting technique of these spiders.

I have denoted this species as 'Mallee" simply because that is where I found them, although each was on a sandy inclusion with a number of heathland species. The first was encountered at 45 km (28 miles) north of Esperance, whilst the other was 110 km (68 miles) NW of Esperance and were discovered during October/November. Maybe arachnid enthusiasts can just go looking and find these spiders, but I must rely on accidentally crossing their paths when looking at the vegetation, so for me to encounter two of them within a week or so, I suspect they might be common in these more arid inland locations.

Flower Spider - Thomisidae - Diaea species

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Flower Spider - Diaea sp.

A large family of spiders with over 140 species in 27 genera and 3 sub-families. The Flower Spiders (also known as Crap Spiders due to the orientation of their legs, permitting them to move sideways) are generally small and colourful, with their front pair of legs very much longer than the latter pair. These are held out wide in preparation to grasp any insect prey that may alight on their flower, which they then subdue with a bite. They do not build a web, but lie in wait to ambush prey, in which they are aided by their bright colors that usually blend with the color of their flower.

Like the Flower Spider's prey, I did not at first notice them (in the photos above) and only saw the large Spider Orchid, Caladenia longicauda. It was not until they moved due to my handling of the flower did I spot them. A male and female Diaea species engaged in a little loving, were initially in the rolled orchid labellum along with a larger honey bee they had captured and stashed there, but my desire to get a photo with the orchid draped over my hand was not to their liking.

The flower spiders from the genus Diaea are usually no more than 1 cm (3/8") in body length, although their legs, particularly the front ones, will easily triple this dimension. There are around 40 Flower Spider species in Australia, of which 8 are recorded for WA. They are not known to be harmful or aggressive to humans and usually drop from the flower when disturbed.