The main threats to the Cromwell chafer were formerly habitat destruction, but now are introduced predators.
The habitat of this beetle is an area of low sand dunes on the Cromwell river terrace, known as the “Cromwell shallow sand”. The dunes are formed by loess originally deposited by the Clutha River, the dunes themselves are the finest inland example in New Zealand. As P. lewisi seems to be adapted to burrowing in these inland dunes, its entire natural range was probably never more than 500 hectares.
You are unlikely to see a chafer beetle here as they only surface from the top sand layer at night in late spring/early summer when the temperature/humidity is just right. The come to the surface to eat and mate. As adults they eat mostly speedwell (Veronica arvensis), sheep's sorrel (Rumex acetosella), and cushion plant (Raoulia australis) They spend at least one year as larvae, living buried in the sand and feeding on plant roots. Males emerge slightly earlier in the year than females, on average.
Animal and plant pests here are controlled to help maintain the habitat. Old rabbit holes have been filled in as they are believed to make fabulous homes for the introduced redback spider thought to have arrived in the 80's. Other predators are earwigs, centipedes and carabid beetles. Little owls and rats and hedgehogs may also pose a threat.
The chunky brown Cromwell chafer beetle Prodontria lewisii itself is about 15mm in length. There are estimated to be about 3000 bettles in the reserve. This large beetle has pale reddish-brown elytra which are strongly convex and with deep groves passing along their length. Females are longer and wider than males, but males have a longer hind foot and tibia.
There is an annual survey of Cromwell chafer numbers – on "Cromwell chafer beetle day" – by DOC and Agresearch, conducted by taking 670 core samples of sand in the reserve and checking them for beetle larvae. They usually find only a few larvae.
Agresearch have in a laboratory in Mosgiel eggs and larvae should anything happen to these beetles.
Have a read of the sign at the entrance from Bannockburn Road. You can walk or drive down the track and do not need to enter the reserve to retrieve the cache.
You can combine this cache with RowenaD's Vegetable Series.