DRB June 2017 Meeting
Mick Davis from the Shire of Kalamunda was our guest speaker for the June meeting about spiders. Mick, a graduate of Curtin University in Natural Resources management, is head of the Shire’s Environmental Friends group and his talk continues the theme of focussing on natural history in the Perth Hills. This was a well-attended meeting with many visitors and members.
Spiders are probably one of the most familiar invertebrates to be found in our homes and gardens and are commonly considered—especially by youngsters—as poisonous and fearsome! Mick’s well-illustrated talk dispelled many myths about spider danger and presented an interesting introduction into some of their general activities and habits.
Spiders can be long-lived, with one individual (a trapdoor spider) known from field research to be more than 30 years old. Spiders are arachnids (Class Arachnida) that are eight-legged, terrestrial arthropods (jointed legs), and have a worldwide distribution that includes most terrestrial environments. All spiders produce silk; some spiders spin webs to catch prey, but silk is used in various ways such as catch nets, cocoons, wrapping prey, lining burrows and as a means of distribution—to float away with the wind. Sexual dimorphism is common, with male spiders often small in comparison to females. Males often have longer legs and shorter bodies than females.
Mick’s particular interest is spiders of the Mygalomorph group (Infraorder Mygalomorphae); these are the most ancient group and are estimated to have existed for more than 360 million years. Approximately 13 per cent of Australian spiders belong to this group, of which there are 2600 species, classified into over 300 genera and 15 families. Two important identifying physical features of spiders of this group are two pairs of ‘book lungs’ (stacks of alternating air pockets and tissue filled with hemolymph, the arthropod equivalent of blood) and downward-pointing fangs (chelicerae).
The other major grouping of spiders that evolved more recently is the Araneomorphs, characterised by having one pair of book lungs and inwardly pointing fangs.
Mick introduced some of the well-known groups, including the Redbacks, Funnel-webs, Peacock Spiders, Huntsman, Orb-weavers and Trapdoor Spiders and gave their salient points interest.
The Peacock Spiders (Genus Maratus) are hunters; they are jumping spiders, using stereoscopic vision to locate their prey and are well known for the males’ multi-coloured, iridescent abdominal flaps. Research has identified that the some colours are generated by a complex combination of pigmented areas and light scattering and others from specific wavelength reflection within the nanostructures of these flaps. Peacock Spiders are a YouTube sensation, however they make their colours!
The Golden Orb-weavers (an araneomorph of the genus Nephila) occur Australia-wide and remain in their constructed large orb-shaped webs spanning several metres. Their silk is a yellow colour and gives the common name to this group. Catching prey in the web is opportunistic but unusual examples of prey include a bird.
The venomous Redback Spiders (Latrodectus hasseltii) are common in our neighbourhood. Their presence is sometimes signalled by noticing a single vertical silk line. Although generally recognized by the red stripe on the abdomen, there are also insects that are similarly marked.
Trapdoor Spiders construct a burrow with a hinged trapdoor. Burrows are known to reach depths of up to one metre and there may also be secondary chambers that help prevent flooding when rain fills the burrow. Gaius villosus also constructs a silk barrier in its burrow that helps protect it from being preyed on. The burrows of trap door spiders, although fairly common, can be difficult to find. Field research, conducted over linear transects (such as 50 m lines), is used to establish burrow density, sizes, distribution and the general health of spider populations. These spiders are also preyed on and eaten by a large number of animals including bandicoots, centipedes, magpies and other birds, other spiders, lizards and Pompilid wasps.
Huntsman spiders are so called because of their speed and mode of catching prey; they are members of the family Sparassidae and some members attain large sizes (to 30 cm diameter). They locate their dens by visual means and their bites can cause trauma.
Spiders are also suitable to keep for observation and one of our young members brought along some examples of spiders in transparent boxes. Mick led a spider search in Jorgensen Park after the meeting. This was mainly to look for Wolf Spiders, which have two larger eyes in front of their cephalothorax, above a curved row of four smaller eyes and another pair of small eyes. The large eyes are conspicuous in torchlight.
Recommended online resources include the ‘Atlas of Living Australia’—or its ‘Ozatlas’ app for your mobile phone—which is an interactive compendium of the natural world for Australian wildlife. The atlas database promotes citizen science and sharing of information; images can be uploaded together with GPS positioning. The distribution of species can be viewed on nationwide maps and global biodiversity information is included.
Recommended reading includes the recently published
Field guide to spiders of Australia
by the CSIRO.