Beehives put into Wisbech Castle as part of a conservation project were destroyed by “brain dead morons” who broke into grounds overnight.
Castle committee chairman Cllr Steve Tierney said the offenders were youths who "found the bee hives, kicked them over, smashed them, and attacked them and the bees with sticks.
"There was no reason to do this, there was nothing to be gained; it was simply to destroy bee hives and bees for some sort of sick pleasure of destruction."
Cllr Tierney said: "A report has been made to the police. We have CCTV of the whole thing. We hope these morons are caught and punished. It is lucky for them some of the volunteers did not catch them in the act."
However a resident posted on the Castle Facebook page that she had called the police at 5.35am "to report that I could hear them in the castle grounds.
"Wish I could have done more. I'm sickened at what they have done."
Cllr Tierney responded to the resident by noting that knowing she had made the call "makes it even sadder if the police were called while it was going on and it still happened".
Police said they received a report of criminal damage taking place at Wisbech Castle on Museum Square during the early hours of this morning (January 8).
"An investigation has been launched and officers are keen to hear from any witnesses who were in the area at the time."
Cllr Tierney said volunteers are repairing the damage although "there is little doubt that we have lost a number of bees and the conservation project has been set back".
Three hives were introduced in July 2019 as part of a black bee conversation project to protect the endangered species and a beekeeper's club for adults and children was launched.
He said the castle has "fairly comprehensive CCTV but when people are wearing coats and hoods, or the video is at range and they are fast-moving CCTV is not as effective as you might think".
He said it added to a list of break-ins that included the theft of gifts bags from Santa's grotto in December and a fairy walk for children was smashed earlier.
Cllr Tierney said "ridiculous and counter productive" heritage laws prevented them taking proper security measures.
"Some wall spikes, anti-climb paint and other counter-intrusion measures would make this much easier," he said.
"If we are worried about damage to the ancient wall, you should see the damage that is being done to it by full-grown adults and large youths climbing over it all the time.
"Volunteers are very angry. We won't be resting on this and will be having an urgent meeting to discuss countermeasures."
Anyone with information should call police on 101 or report online via www.cambs.police.uk/report quoting crime reference number 35/1817/20.
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