Chafer bee­tles’ over­seas at­tack

Central Otago Mirror - - YOUR PAPER, YOUR PLACE - RHYS CHAM­BER­LAIN

They are the stuff of night­mares - the arach­nid with a men­ac­ing red stripe and enough venom to kill a per­son.

The Aus­tralian red­back spi­der has found the per­fect home-awayfrom-home in an 81 hectare na­ture re­serve in Cromwell, Cen­tral Otago.

Univer­sity of Otago re­searcher Jackie Spencer says it’s per­fect due to the hot, dry cli­mate, an easy-to-catch food source and rabbits.

The re­serve is also home to the crit­i­cally en­dan­gered Cromwell chafer bee­tle, the only place in the world the bee­tle lives.

Now new re­search led by Spencer has con­firmed red­back spi­ders are us­ing empty rab­bit holes as an easy way to catch and de­vour the chafer bee­tle, threat­en­ing their ex­is­tence.

‘‘We al­ready knew that they were in the re­serve. It was whether they were build­ing their webs in old rab­bit holes and whether the rabbits were aid­ing the red­back spi­ders,’’ she says.

Spencer recorded and an­a­lysed prey caught in red­back webs in the re­serve over a four-month pe­riod and stud­ied what im­pact fill­ing in rab­bit holes had on spi­der pop­u­la­tions.

Her re­search found 99 per cent of red­back spi­ders in the Cromwell Chafer Bee­tle Na­ture Re­serve had built their webs in old bur­rows and the chafer bee­tle was the sec­ond-most com­mon prey found (the most com­mon was the dark­ling bee­tle).

In Spencer’s first sur­vey in 2014/15, GPS track­ing con­cluded there were at least 550 red­back spi­ders in the re­serve, most con­cen­trated around clus­ters of un­used rab­bit holes.

The rea­son for this is that the rab­bit holes pro­vide the ideal place for red­backs to build webs to catch the bee­tles and re­pro­duce, Spencer says.

Over a two-year life­span a sin­gle fe­male red­back typ­i­cally pro­duces four egg sacks a sea­son each con­tain­ing about 200 spi­der­lings, she says.

Af­ter re­mov­ing 15 fe­male spi­ders from rab­bit holes, fill­ing them in and re­leas­ing the spi­ders, four months later none were liv­ing in the vicin­ity of the filled-in holes..

Spencer’s lat­est count put num­bers at about 112 fe­males largely thanks to her ef­forts.

‘‘We can def­i­nitely cut the num­bers back [but] the spi­ders are def­i­nitely still there and I think it’s go­ing to be an on­go­ing bat­tle re­ally.’’

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