Overview
Scientific name: Family Thomisidae, subfamily Stephanopinae, Sidymella spp.
What do they look like?
As the name suggests, square-ended crab spiders do not have the rounded abdomens typical of the majority of spiders. When viewed from above, the upper surface of the abdomen looks a little like a trapezium. New Zealand endemic species such as Sidymella angularis are rather gnarled in appearance and come in various colours including shades of brown, grey and yellow. The two exotic species established in New Zealand (Sidymella longipes and S. trapezia) are comparatively smooth-looking and are predominantly pale brown in colour. The first two pairs of legs are the longest and are armed with strong spines. Sidymella angularis is the largest species with adult females reaching up to 12 mm in body length.
Where are they found?
With the exception of one undescribed species from the Far North of New Zealand, the other endemic species can be found throughout much of the country in habitats ranging from gardens to native bush. They are common in leaf litter and are often found on ferns and grasses. The Australian species S. longipes is found in modified habitat in the upper North Island while S. trapezia is most commonly encountered on lower North Island coasts.
What are their habits?
New Zealand square-ended spiders are ambush predators rather than web builders and lie in wait for their prey. The first two pairs of legs are powerful and strongly spined. They are used to grab and hold victims before biting. Several species are known to play dead when disturbed, drawing the legs tightly in against the body and giving the appearance of a small piece of bark or debris. Females typically attach their egg sacs on the undersides of dead leaves. Sidymella trapezia appears to be an exception and egg sacs are bound to grass stems.
What is their bite like?
Unknown, but unlikely to cause anything beyond minor discomfort.