SERIES: Invertebrate of the Week

Invertebrate of the Week #5 – Opadometa sarawakensis spiders

Allow me to introduce a conspicuous group of spiders from Southeast Asia.

According to photographer Alex Hyde, who took the gorgeous macro images below while working in the Maliau Basin (Sabah, Malaysia), this spider is a member of the genus Opadometa; a group of spiders colloquially called long-jawed orb weavers.

Opadometa sarawakensis spider colloquially referred to as a "long-jawed orb weaver."
Opadometa sarawakensis spider; a type of long-jawed orb weaver.
Image by Alex Hyde | http://alexhyde.photoshelter.com/

Spiders of the genus Opadometa (family Tetragnathidae) are currently represented by at least four species (and one subspecies) found in the Southeast Asian tropics. They typically occupy vertical or oblique orb-type webs (~ 30 radii; ~30 spirals; open hubs) in shaded vegetation near roads or streams.

While the stunning coloration obviously catches the eye, you might also be struck by the brush-like tufts of macrosetae on the distal third portion of the tibia. The presence and arrangement of these setae are actually one of the defining characteristics of the genus. Though I was unable to find any literature as to their exact utility in this spider, I would venture to say they serve some sort of sensory function.

As for the exact species in the above photo, it’s clear that it is Opadometa sarawakensis and that it is a female. On a side note, this is a relatively newly described species. It appears that it first formally appeared in the literature in 2014 (Koh and Ming, 2014) and wasn’t described until 2015 by Dzulhelmi et. al.

The difference in size and appearance between males and females of that species is extreme. Female Opadometa sarawakensis are quite large, reaching at least 8.1 mm long based on field measurements in the available literature. That makes them more than twice as long as males (female/male size ratio = 2.2). Field notes from Miller, et. al. (2018) suggest that the only web weaver spiders larger than female Opadometa sarawakensis in their natural habitat may be members of the genus Nephila – a genus of spiders that grow large enough to catch small bats and hummingbirds.

Females are also much more colorful than males. A male Opadometa sarawakensis is a dusky orange and brown color. You’d probably hardly notice it next to the larger, more eye-catching female.

Female Opadometa sarawakensis lateral view, with male to show sexual size and color dimorphism.
Female Opadometa sarawakensis lateral view, with male to show sexual size and color dimorphism
Image from Dzulhelmi & Suriyanti, 2015
Female Opadometa sarawakensis live specimen
Female Opadometa sarawakensis live specimen
Image from Dzulhelmi & Suriyanti, 2015

This post was updated from the original version published in 2014.

References and Further Reading

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