Question. Why is a brightly coloured insect called a soldier?
Soldier beetles are so called because of their bright high contrast colours. The name emanates from the UK of course, where many species are bright red – the standard colour of the old British Army ‘red coat’ uniform, in the days when soldiers identified each other by their colours in the fog of war. And soldier beetles are pretty aggressive too – put one in a vial with another insect and there will quickly only be bits and a fat soldier beetle.
Soldier beetles all belong to the family Cantharidae. In the UK there are many colourful species and most are quite large and conspicuous, as they like to sit on flower heads. Here in Australia we have about 200 species but many are small and only a few are conspicuous. One of these is the ‘plague soldier beetle’, Chauliognathus lugubris. From around this time of year to Christmas I get enquiries about swarms of these in people’s gardens around Sydney. The beetles are not eating plants and are harmless (unless eaten) and the swarms are basically just mass mating opportunities.
Best not eaten – the bright colours and their slow flight tell you that these are poisonous.
Most species of Australian soldier beetles are much smaller and generally black with a red front end (head and part of thorax). These belong to the genus Heteromastix. Males of Heteromastix can be distinguished by having strangely swollen segments of their feelers (antennae). The antennae are their noses and males have these enlarged segments to pick up the scent of females. I think male humans generally have larger conks than females too.
Heteromastix is also commonly found on flowers, especially tea-tree (Leptospermum), but not in large numbers. Little is known about this genus, probably because the beetles are small, only about 5mm long. So, treating 2508 as a citizen science journal, I can report here a new observation, on my driveway.
We normally have a few flying around slowly and apparently aimlessly every spring. But this year there was a swarm of about 200 of them flying and crawling around one spot on the concrete. When I poked at the aggregation, I found they were crawling all over a small millipede. And the four specimens I sampled were all males. I collected the millipede, thinking they must have been eating it, but it was undamaged.
What was going on? Actually I have no idea, but here are three hypotheses.
1. The millipede’s chemistry was similar to a female beetle and the males were making a bad mistake.
2. The beetles were stealing the millipede’s defence chemicals, by licking them up, and using the chemicals for themselves. But why no females?
3. They were having a party.
I’m inclined towards either one or two. What do you think?
For general insect enquiries, visit australianmuseum.net.au/learn/species-identification/
