Sheep in Wolf’s Clothing

Insects that are armed with powerful stings are often strikingly coloured to warn off potential predators – a strategy known as aposematism . A good example of this is the black and yellow colour pattern of the European wasp (Vespula germanica).

Vespula germanica

Some harmless insects take on the appearance of aposematic insects even though they are not actually dangerous themselves. Hover flies are an example of this. One common hover fly species the drone fly Eristalis tenax – is an excellent bee mimic, and was the star in a recent ‘one minute bugs’ video (link).

Other common hover flies (image below) are harmless flower visitors but their striking yellow and black markings superficially resemble the markings of bees or wasps. Bees and wasps usually have stings and consequently are left alone by many predators. Hover flies don’t have stings, so by adopting colour patterns similar to bees and wasps this affords the hover flies some protection. This defence strategy is known as Batesian mimicry.

Bee mimic

Now for a wee bit of history. H.W. Bates (hence ‘Batesian’) was the first scientist to conduct a major study on mimicry – in the Amazon Basin in the 1860s. Charles Darwin recognised Bates’s work on mimicry as critically important to the theory of evolution, and cited it extensively in later editions of his own great work The Origin of Species. Darwin appears to be quite a fan, because in a letter to Bates in 1862 Darwin wrote:

“Dear Bates. I have just finished, after several reads, your paper. In my opinion it is one of the most remarkable and admirable papers I have ever read in my life.  .  . Your paper is too good to be largely appreciated by the mob of naturalists without souls; but, rely on it, that it will have lasting value, and I cordially congratulate you on your first great work.”

I am particularly intrigued by insects which mimic other insects that would normally appear very different from their own body shape. It’s easy to see how a yellow and black patterned fly could look like a bee or a wasp (e.g. the hover fly), but how about a beetle which looks like a spider-hunting wasp? The yellow-horned clerid beetle Trogodendron fasciculatus (Cleridae) – image below – mimics the spider-hunting wasp Fabriogenia sp. (Pompilidae) – lower image.

Trogodendron

If you place them side-by-side you might think the resemblance is only superficial – dark bodies and yellow/orange antennae. It’s when they move that you see mimicry at its best. Spider-hunting wasps move in a characteristically jerking manner and flick their antennae constantly as they look for spiders. The yellow-horned clerid beetle mimics these movements exactly, so much so that when you see one moving you would swear that it is a wasp. The beetle would then be completely safe from predators especially spiders. No sane spider would want to go near an insect that appears to be a spider-hunting wasp!

Spider wasp
Share this:
Facebooktwitterlinkedinmail

Return of the Green Scarab

Green scarab beetleDuring November swarms of green scarab beetles (Diphucephala colaspidoides) descended on my place. They are notorious leaf eaters noted for stripping the leaves from a variety of plants. The beetles tend to feed in large groups so plant damage can happen quickly and be quite devastating. Can plants recover after such damage?

Back in the 19th century these beetles were known as “cherry green beetles”. Just listen to how Charles French, the government entomologist of the time, describes their attack in his Handbook of the Destructive Insects of Victoria. “When they make their appearance in an orchard, which is about “cherry time”, they make sad havoc, and, being in such countless multitudes, will strip a good-sized tree in the course of a very few minutes”.

The swarms did indeed make sad havoc of a few plants on my property including Melaleuca pentagona, Leptospermum continentale, and Acacia mearnsii. The tea trees were severely chewed leaving some plants looking like they were suffering from drought, the top half of a melaleuca turned brown, and several acacias were semi-defoliated. This all sounds rather alarming but what happened next is worth reporting.

Over the last couple of months the plants have mostly recovered, and the M. pentagona is positively booming. I don’t see these beetle every year, in fact I haven’t seen them in such numbers since the spring of 2006. I know they are only feeding so they can mate and lay eggs, after which they die. Even if I wanted to control them chemically I would be out of luck, because there is nothing registered against them.

Green scarab beetlesAs we have seen, green scarab beetles like to feed on tea-tree (Leptospermum spp.) and wattles (Acacia spp.). The generation of green scarab beetles emerging in the spring of 2006 had no tea-tree or wattles to feed on as most plants had been burnt out in the massive Grampians bushfire of January 2006. The beetles had to feed on something and appeared on various properties in enormous swarms causing some headaches in commercial vineyards and orchards. They completely defoliated some plants, but the swarms soon moved on or died.

Green scarab beetles have a life cycle typical of most scarabs in that their larvae feed underground on the roots of various plants. That’s why the larvae weren’t wiped out by the bushfire (heat tends to go up, not down) and were able to emerge as adult beetles months later. Adult female beetles need sufficient nutrition from sap or nectar to lay fertile eggs. I hardly saw a green scarab beetle for several years after the 2006 swarms. I can only assume that many females of that particular generation didn’t get enough nutrition from the plants (vines and berry crops etc.) they had been feeding on to lay fertile eggs. The tea-tree and wattles have now largely regrown which is probably why the green scarab beetles have returned.Share this:
Facebooktwitterlinkedinmail