The Perching Dung Beetles of Wongabel

On a recent nocturnal photographic trip to Wongabel Arboretum, not far from Atherton, north Queensland, we noted number of perching dung beetles on foliage after dark. This is not an uncommon observation in tropical Australia but I was surprised to discover from colleague, Tom Weir, that three friends had written about this phenomenon some years ago.

Howden et al. (1991) reported that they found some 22 species of Scarabaeinae dung beetles at Wongabel.

A perching dung beetle, Onthophagus dicranocerus Matthews on Lantana at night. Body length approx. 11mm.

It seems that in the New World Tropics, dung beetles sort themselves on their perches by size. That is, the smaller species are found closer to the ground than the larger ones.

So the Howdens and Ross Storey recorded the height on each perch for 561 individual dung beetles at Wongabel. [Something for you to do on a dull night, but we did not observe anyone else in the rainforest measuring dung beetles or doing anything else for that matter!]

They discovered that there is no clear evidence at Wongabel that the smaller species positoned themselves closer to the ground than the larger ones.

A female O. dicranocerus atop a leaf and waiting to pick up a signal that dung is near through sensory receptors on her antennae.

Why do these beetles perch? It is most likely for the detection of fresh dung, be it from Wallabies, possums or other mammals or, perhaps, birds. But oddly enough, perching seems confined only to the dung beetles in tropical rainforests. Elsewhere in Australia they do not perch at night.

A male O. dicranocerus partially disturbed by me and the falling rain. His antennae are partially withdrawn. Note the paired projections off the head that gives the species its name.

The typical perching behaviour for rainforest dung beetles is with the lamellate antennae extended and flared.

The lamellate antenna of one of the dung beetles poised to pick up scents of a potential feast or sex!

Some general observations by the Howdens and Storey

1. The beetles preferred smooth, shiny leaves and seemed to avoid aroids and hairy or spiny leaves. [Having an experience with the nettles of Wongabel, I can agree with the dung beetles!] 2. Perching occurs on rainy or clear nights.

3. There is no stratification for height of perching based on the size of the beetle.

4. The five common perching species perched, on average, below the 60 cm level and all averaged under 10 mm in length.

5. Some generic differences were noted.

6. Australian native species shared no lineages with other continents.

7. In time the Wongabel perchers have had to shift their food preference from dung of other mammals to marsupials.

8. The perching habit of Australian beetles may have evolved independently from those of the New World.

9. Perching in some species seems to be a foraging strategy.

A note: It shows what can be accomplished with a little thought and a specialization in a group of insects. With the current trend towards the diminution of taxonomists, this sort of thought process will be lost.

Thanks to Tom Weir for comments.

Literature.

Howden, H. F., Howden, A., Storey, R. 1991. Nocturnal perching of scarabaeine dung beetles (Coleoptera, Scarabaeidae) in an Australian tropical rainforest. Biotropica, 23(1): 51-57.