The 10-spot pot beetle (Cryptocephalus decemmaculatus) is a bit of a mouthful and it is also very rare. The only known site for this leaf beetle in England is within the 16.5 hectares of Wybunbury Moss National Nature Reserve (NNR), located towards the southern border of Cheshire .
There are nineteen Cryptocephalus species found in Britain and many of them are of conservation concern. The adults of the genus are fully winged, thermophilic and can be found perching on their respective host plants. They have a fascinating life cycle in which the female beetle encases each egg she lays in faeces. The eggs are dropped onto the ground and, once hatched, the larvae adds to the egg case to form a larval case, which it carries around and retreats into at the first sign of danger. Larvae of all the species feed on leaf litter, making them vulnerable to habitat ‘clean-up’ management. They eventually pupate from the larval case and make a short flight up into the leaf layer.
Cryptocephalus decemmaculatus is a yellow, black spotted leaf beetle. The adults are small (4-5 mm long).
Dr Ross Piper is an expert on the genus and has made some very interesting discoveries aboutCryptocephalus decemmaculatus, finding that the beetle depends upon dynamic scrub transition and adults are found predominantly on small Salix spp. trees invading areas of wetland. The beetle moves through its habitats using suitable host-plants as ‘stepping stones’. These beetles cannot fly well and there appears to be no interchange of adults between sub-populations that are separated by small areas of unsuitable habitat, a deduction reinforced by other studies of their genetic differentiation over distances as small as <1km.
Ross believes that the beetle population at Wybunbury Moss was isolated when surrounding land made way for agriculture, many thousands of years ago or possibly even when the surrounding land became drier in the post-glacial period.
Wybunbury Moss is one of only two types of special ‘subsidence formed moss’ known to exist in the British Isles. Peat has been deposited in a glacial hollow but has actually formed a raft, in some places only a metre thick, which floats on a water-filled basin itself over 12 metres in depth. It is believed that the floating nature of the Moss may have been created by the subsidence of salt-bearing rocks beneath the Moss basin. The site is managed by Natural England.
During my involvement with Natural England, it has been fascinating seeing how the balance in habitat management is achieved with tree and scrub removal to reduce the drying out of the Moss whilst maintaining and encouraging the host trees for Cryptocephalus decemmaculatus. The objective is to provide habitat corridors for the beetle to move ‘via a series of short flights’ into different suitable areas of the Moss, thus making in less vulnerable to the vagaries of factors impacting micro-sites.
Wybunbury Moss, together with its surrounding woodland, reedswamp and flower-rich meadows also provides habitat for a rich variety of uncommon plants and animals, including two Nationally rare spiders.
Wybunbury Moss is, however, a dangerous environment and there is no general public access to the site. A public footpath surrounds the NNR, giving good views across the Moss. A visit to the site in September 2012 is included in the CAN Events Calender 2012/13 in which we will be venturing onto the Moss with guidance, so why not join us to experience this unique and special habitat?
While Cryptocephalus decemmaculatus is only known to be found at Wybunbury Moss, it is possible it could be present at other sites where there is scrub transition between woodland and wetland. Late May to early June is the best time of year to see the colourful adults so keep an eye out!
Many thanks for the information contained within this article to:
Dr Ross Piper
Ruper Randall (Natural England)