Bug bits: The truth about Christmas beetles in Darwin

WITH Christmas and New Year’s behind us again, it’s time again to pause in reflection. In reflection, that is, about the myths surrounding Christmas beetles and Darwin

Kate Brown and Dr Graham Brown. Picture: Justin Kennedy

WITH Christmas and New Year’s behind us again, I — like many others — have paused in reflection.

Although, I reflect somewhat differently to others and wonder about the myths surrounding Christmas beetles.

It is a common belief that Darwin is home to Christmas beetles.

However, those prickly-legged, noisy, grey blurs that fly into ceiling fans and catapult against our walls are not technically Christmas beetles.

Even if they turn up at Christmas.

Anoplognathus macleayi, it is a common belief that Darwin is home to Christmas beetles.

Christmas beetles are scarabs (family name Scarabaeidae) and belong to the genus Anoplognathus.

This genus is represented by more that 30 species, none of which reside in Darwin.

In fact, in the Territory, Christmas beetles have been recorded only as far north as about Borroloola.

Christmas beetles are relatively large with strong spiny legs that are used for digging.

Similar to most scarabs, the top is rounded (convex) in cross-section.

Unlike Darwin’s scarabs, the colours of Christmas beetles are much more vibrant, and, depending on the species, are variably yellow, golden or bright metallic green.

There are a lot of scarabs in the Northern Territory, but the most common scarab seen in Darwin is Lepidiota (especially L. squamulata).

Lepidiota is a beetle of the Scarabaeidae family

These beetles are unmistakably brown and covered in flat white scales and tend to emerge about the same time as the first rain.

Another local species — Ischiopsopha — emerges a little earlier, flies much faster and is more active during the middle of the day.

This species is also likely to be mistaken by some as a true Christmas beetle.

You may be able to identify Ischiopsopha because, although it is bright metallic green, the top of the body is distinctively flat.

Of course, that’s if the beetle sits still long enough to be recognised.

Ischiopsopha are beetles from the subfamily Cetoniinae

Scarabs produce one generation per year with adults appearing in Spring to early Summer; however, most of the year is spent as a larva feeding and growing.

Eggs are laid into the larval substrate, which is often soil among grassroots. 

Regardless of species, larvae all look the same to the naked eye: a C-shaped grub with a darker head and tail.

When fully fed (on decaying logs, other plant material or even dung) larvae pupate in the same substrate or small hollow they have created.

The pupa looks like the adult, but white with visible appendages adhering to the body.

Pupation takes only a few weeks before adults emerge, whereby most are commonly seen in the early evening on warmer, stiller nights.

Lepidiota larva

Recently, there have been discussions regarding a significant decline in Christmas beetle populations, particularly around the Sydney area.

While scientific evidence is limited, any reduction is likely to be resultant of habitat loss and localised insecticide use.

Christmas beetles tend to almost exclusively feed on eucalyptus leaves as adults, and with increased urbanisation and reduced food supply many species are sadly impacted.

With regard to the Darwin scarabs, which tend to emerge in the first rains, it is possible that our scarabs have also suffered due to the absolute lack of rain this wet season.

If you have noticed a change in the habits or frequency of insects in your area or have found something you would like identified, I’d love to hear about it.

• Dr Graham Brown and Kate Brown ([e-mail])