Successful breeding and release of the Hazel Pot Beetle
We are very pleased to report that our captive stock of the RDB1 (Endangered) Hazel Pot Beetle Cryptocephalus coryli, have successfully over-wintered and bred.

With a few adults still to emerge, we released almost 1,000 beetles in Sherwood Forest on May 12th 2014, reared from a total of 1,166 pupae.

The release will help augment the Sherwood Forest colony, from which eggs were originally obtained in 2011 and the resulting adults bred from in 2012. We have retained several thousand eggs for continued breeding purposes and further release, which should emerge as adults in Spring 2014.

Although larvae can be mature within a year, keeping them outside and going with the natural two year life-cycle, resulted in better quality stock.

Captive breeding set-ups

After emergence, the adults were transferred to a large bucket, netted over and kept outdoors (weather permitting) during the day, but returned indoors overnight. It soon became obvious that one bucket would not suffice, so emerging beetles had to be housed in a second identical set up.

As more adults continued emerged, a third set up soon became necessary, until we eventually had to transfer them all to one large plastic container, which was similarly netted over and a door cut into the side of the container to allow access to change the foodplant ever two or three days as required.

The system worked extremely well and we had very few casualties, despite our efforts to ensure the water filled jars holding the Birch foodplant, was tightly blocked off.

Adult emergence

Emergence was largely restricted to a period of about two weeks from April 26th and by the time of writing (May 12th) was virtually complete. We were extremely pleased with the emergence success rate of 82%.

After single males emerged on April 26th and 27th, two males emerged on April 28th, before 24 adults (including the first five females) appeared on April 29th. The largest number to emerge on a single day was 156 on April 30th. Numbers of emerging adults has steadily declined since, although 126 adults emerged on May 3rd.
Peak time of day for emergence was found to be early afternoon, but beetles would emerge from first light and continue into the late evening.

Light and probably temperature, seemed to induce emergence and artificial light after a period of natural darkness, would see continued emergence into the early morning hours.

The first egg containing pots began to appear after a few days and the adults habit of chewing through the leaf stalk, soon meant that the bottom of any containers had a thick layer of leaves. In most cases, the adults bit the leaf off, while they actually sitting on it.

Flight in all containers was much stronger and direct than we had previously believed and it seems quite clear to us now, that outward spread of any population is distinctly probable, given the availability of suitable habitat nearby.


Release of nearly 1,000 Hazel Pot Beetles took place at the Sherwood Forest Country Park on May 12th 2014. The location of release was within the boundaries of the existing colony, which was rediscovered after a 70 year absence back in 2008 and from where the parents of the released stock originated from.

Rearing Cryptocephalus beetles in captivity