The other day I heard a deep hum (sounding like that produced by a large bumblebee queen) and saw that it was came from a large green iridescent beetle flying around a flowering pyracantha. I waited for it to land excitedly, as I was pretty sure of what it was, and eventually the beetle landed on the flowers: as I expected it was a Rose Chafer, Cetonia aurata, my first one in Hull. I searched the bush and found at least four other individuals, feeding on the flowers. An hour later, as I returned from my walk I checked again and found a mating pair. Rose Chafers are a charismatic, jewel-like species. They are about 2 cm long, burnished metallic green and have variable wing markings, formed by whitish squiggles on the elythra. The species is not particularly widespread in the UK, and has an unusual patchy distribution, mainly in the south, with scattered coastal populations. It is often associated to urban environments such as gardens, parks and allotments.
A Hull population
I checked the NBN Gateway Atlas and iRecord for the species and was surprised to find that Hull appears to hold the only Yorkshire population of this species. There is one record from a private garden in Fulford, York in June 2019 and another from Bradford in June 2013. The 11 Hull records span the last 16 years (from 2020) all in a residential, leafy area of about two square km known as The Avenues. The records, all of adults, were submitted by 10 different observers, highlighting that it is a conspicuous species, with adults hard to miss. The records are from May to October, with a peak in July, which mirrors the adult flight period. The geographical tightness of the cluster suggests that this is a discrete established population. The origin of this population is intriguing, given the absence of nearby colonies, so an accidental introduction with compost or plant pots is a strong possibility.
Life cycle
The larvae take one year to complete their development in old wood, logs, stumps, compost piles, wood chips or leaf litter, decomposing these materials into rich mould. Occasionally they are found in pots including hanging baskets, where they are likely to be attracted to the compost, but they are not thought to feed on live roots or damage the plants. Larvae of some coastal populations feed on peat under coastal turf. They pupate around mid summer in a rounded, bumpy cocoon made of their faecal pellets. Adults are usually formed in August, but usually only emerge after overwintering in the following April or May.
Behaviour and ecology
Rose Chafers fly in warm, sunny weather, and around the middle of the day, in search of flowers and mates, producing a deep bumblebee-like hum. They fly with their wing-cases closed and a modification of their elythra allows this. The adults feed on nectar and pollen, favouring mass flowering plants on sunny aspects, with umbel-like open flowers, including hogweed, guelder-rose hawthorn, but also artichokes, and cardoons. Their hairy underside attracts pollen and they are pollinators of the plants they visit, as they move clumsily around an inflorescence and by flying between plants. Their name, however, comes from their penchant for eating petals ('chafing') of some rose cultivars. Populations might benefit from warming weather given the adults activity patterns and the current distribution.
More information
Fremlin, M. The Rose Chafer Cetonia aurata L.(Coleoptera: Scarabaeidae: Cetoniinae) in Essex: distribution and some aspects of its ecology. Essex Naturalist (New Series) 35, 167–178 (2018).
Maria Fremlin webpage on Rose Chafers.
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