Golden-bloomed Grey Longhorn Beetle

The Golden-bloomed Grey Longhorn is a stem boring insect whose name accurately describes its appearance.

They have long arching antennae (longer than their body) with black and pale-blue bands. Their pronotum is dark grey with three lateral, creamy-gold stripes. Their elytra have dense pale grey to golden scales forming a mottled pattern and golden hairs that gradually rub off as they age.

It is one of only two UK longhorn species whose larvae develop in the stem of herbaceous plants, other longhorn species use the stems of woody plants.

Adults are diurnal, in warm weather, they can be easily spotted sitting on flowers with their antennae held high over their body. Although they are most often spotted on umbels they can be seen on a wide range of host plants.

Mating occurs during May and June and egg-laying follows shortly after. The female explores selected plant stems, occasionally stopping to chew the plant tissues, until she finds a suitable site.

Once she has chosen a spot she gnaws a hole into the plant stem and lays one, or occasionally two, eggs. She then seals the hole with chewed up plant material.

In spring they feed a little longer and then settle in the plant roots to pupate for about a month. The pupa is also mobile and can move up and down in a hollowed-out cell that is plugged at either end with plant material. After hatching the adult stays in the pupal cell for another week or two before emerging to feed on herbaceous leaves and start breeding.

The larvae emerge after a week or so and quickly grow to fill the central cavity. Rows of tiny bristles on their abdomen allow them to grip the stem from within and rapidly move up and down the stem. They eat the plant stem from within, working their way down to the roots. By late summer they are fully grown and ready to overwinter in the base of the stem or the rootstock.