1 Invertebrata 14 — July 1999 Invertebrata Tasmania’s Invertebrate Newsletter July 1999 No. 14 Invertebrata is produced by the Queen Victoria Museum and Art Gallery, Launceston, Tasmania. We publish articles and short notes on all aspects of invertebrate biology and conservation in Tasmania. All correspondence (including changes of address) to the editor, Bob Mesibov PO Box 700, Burnie TAS 7320 (03) 6431 3428 mesibov@southcom.com.au Inside... Features: Editorial 2 Historical footnote 6 Invertebrates in the media 8 News 4 QVMAG: B. Smith DPIWE: T. Semmens DPIWE: L. Hill Notices and reviews 3, 8 Articles: Anoglypta delisted K. Bonham 5 Crayfish range study N. Doran 6 Crab stranding event C. Gardner 1 Caddisflies rediscovered J. Jackson 3 Fossil insects at QVMAG B. Smith 7 Spider crab on Tasmania’s northwest coast Caleb Gardner In early June large numbers of spider crabs were washed up on beaches at several locations along the northwest coast. There was a lot of public concern, as many people assumed this stranding was caused by pollution or a biological disaster along the lines of the recent pilchard kills. My impression is that the event was far less sinister and was just a natural phenomenon. The strandings followed large aggregations of spider crabs in shallow coastal wa- ters. At Stanley the sea floor around the wharf was completely covered in living spider crabs. So the first issue in understanding the stranding event is to explain how so many crabs came to be in the bays in the first place. Aggregation behaviour in spider crabs is quite common. The species involved in this event was Leptomithrax gaimardii (M-Ed.), which is abundant around Tasma- nia’s inshore coastal areas, particularly on silty substrates. Several species of Lepto- mithrax form aggregations into mounds. This behaviour is seen in numerous spe- cies of spider crabs (family Majidae) worldwide, including commercially important species such as Maja squinado (Mediterranean), Chionoecetes opilio (snow crab, Can- ada), and Hyas coarctatus (Canada). Majids appear to be social animals and I’ve seen large numbers of L. gaimardii moving in scattered groups, similar to the groups of soldier crabs that are common in Tasmania’s intertidal areas. Aggregating appears to occur for several reasons. L. gaimardii is usually found in loose groups as part of normal behaviour, but they frequently form very dense piles up to 1 m deep and several meters across. These often occur when females moult and become receptive to mating while soft-shelled. At other times the mounds con- sist of hard shelled intermoult crabs, so we can only speculate what causes these ‘hard’ aggregations. In the recent strandings, all of the crabs we sampled had either just moulted, or were about to moult. Both males and females were seen so this (continued on page 2) The spider crab Leptomithrax gaimardii