March 2019

Drowned Mouse?

This spider was in my pool. Is it a Funnelweb Spider?

Answer

We’ve recently received many inquiries about Whitebacked Mouse Spiders (Missulena bradleyi). These robust spiders are mygalomorphs, distant relatives of Funnelwebs, Trapdoors and Tarantulas. Mouse Spiders are sexually dimorphic (the sexes are different sizes), with large females and males that are smaller and commonly more colourful. Male Whitebacked Mouse Spiders have a distinctive pale patch at the front of their abdomen. Female Whitebacked Mouse Spiders can only be distinguished from those of other species with some difficulty.

Female Mouse Spiders spend most of their time in their burrows. In late summer and autumn male Mouse Spiders rove about in search of females, and this is when they are most likely to be noticed by humans. A few of these questing males fall into swimming pools or enter low-set houses, causing consternation when discovered. Mouse Spiders can survive submersion for several hours, so spiders found in pools may appear dead, but revive when allowed to dry out.

Mouse Spiders should be treated with caution. Experiments suggest that their venom is highly toxic, and has the potential to be fatal to humans. However, the majority of reported bites did not result in any serious reactions, and it appears that these spiders are reluctant to inject venom when biting defensively.

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