The burrowing wasp

We’ve had a couple of big mounds of mulch in our garden since the stump-grinding people did some work for us almost a year ago. “Leave us some mulch,” I said, and they did.

We have gradually spread it around and dug it in, but we’ve had a surprising amount of help from little friends – mostly big fat white grubs which are scarab larvae.

A big black wasp has been keen to help, too.

Flower Wasp
Wasp digging into the mulch
Black Flower Wasp
Almost gone

I’ve seen one several times in the last couple of weeks, flying up out of the heap as we disturbed it, or circling before landing and digging, but I haven’t managed a clear shot of it on the surface. This old photo, however, probably shows the same species.

As I said at the time, it’s a Hairy Flower Wasp, Scoliidae (I haven’t been able to identify it to species level but the genus is Scolia). They are “flower wasps” because the adults feed on nectar, as this one is doing. (It’s in the same genus but is not the same species – note the absence of yellow spots on the abdomen.) Their larvae, however, parasitise scarab grubs, so my wasp was digging down to lay eggs.

Our most common adult scarab is this beautiful metallic green creature. It’s in the scarab family, as are so many of our largest and most colourful beetles. I know it’s in the subfamily Cetoniinae – Flower Beetles – and it seems likely to be Ischiopsopha wallacei but I can’t be quite sure. In any event, its larvae have been very helpful in breaking down our mulch and are the likeliest targets of our wasp.

green scarab beetle
The beetle whose larvae are the target

Compost critters

Brown Centipede
Centipede

Gardening is always a good way to come across the small wildlife around us and sifting compost can be among the most rewarding jobs in this way because it reveals many critters (‘bugs’, if you prefer) which rarely see the light of day.

Centipedes live in leaf litter and other moist shady habitats, and the one above was perfectly at home in the compost until we disturbed it. And why not? Cool, damp, dark, and full of small insects to eat … just about perfect. It wasn’t enormous but at just under 60mm long it was probably big enough to give someone a nasty nip and was treated with due caution during the photo shoot before being released. For more about centipedes, visit the pages of CSIRO or the Queensland Museum.

Fat white elephant beetle larvae are common in the compost, too, and we sometimes see larvae of smaller scarabs – or even the emerging adult, like this beautiful green one. We saw another of these today but it flew off before I could get a photo. All these beetles spend time underground as grubs and dig their way out after metamorphosing into their adult form. They sensibly wait until the soil softens before doing that, so they emerge in great numbers at the beginning of the Wet; we call the pretty ones Christmas beetles but I’ve got to say they are too late for that this season.

A few days ago I found a large beetle pupa (not a cicada nymph as I first thought and said) when I was emptying a plant-pot which had nothing much in it but weeds. We often see the cast-off exoskeleton of the cicada nymph, hanging on a plant like this with its back split open where the adult has emerged, and the elephant beetle larvae, but I had never seen either a living nymph or an elephant beetle pupa. One big difference which I should have noticed is that the cicada nymph has strong digging claws on its front legs but the beetle doesn’t.

Cicada nymph
Beetle pupa extracted from its underground cell
Cicada nymph on its back
Another view

This illustration of the beetle’s whole life cycle depicts a different species but the resemblance is clear.

Rhinoceros beetle

Rhinoceros beetle on person's hand
Rhinoceros beetle on my fingertips. Both of us were reasonably comfortable.

Our Rhinoceros beetles are amongst our largest, heaviest insects. They grow as grubs underground and emerge as adults during the wet season. They are scarabs – Xylotrupes gideon, Dynastinae, Scarabaeidae, in fact – and the sexes are quite dramatically different. The male, which is what I have in the picture above, has two large horns used in mating battles, the lower one projecting from the top of his head and the upper one from the thorax. The beetle can pinch the horns together, but rather weakly and they can’t harm anything because are blunt anyway. Females, on the other hand, are hornless and a little smaller (you can see both sexes here).

They are all clumsy fliers, often barging into furniture and people when attracted to house lights at night. Some people are timid about dealing with such large, heavily armoured creatures but they are quite harmless vegetarians. The only problem can be detaching them from hair or clothing without hurting them: their legs are long, wave wildly and seem to have hooks everywhere. The best way to hold the males, I have found, is by the horn:

Rhinoceros beetle in the hand
Holding a Rhino beetle safely (for both parties) so that he can be carried outdoors and released

More: Wikipedia and, though not particularly about this species, Animal Corner.