While taking a break on a country bike ride, I saw this unfortunate insect (near right) impaled on the thorn of a low bush. We鈥檇 had strong winds in the days beforehand and I can only assume that the insect was blown onto the thorn, which has penetrated the open wing casing before impaling the body. What are the chances of an event like this occurring?
鈥� The beetle is Phyllotocus macleayi, a nectar scarab common in south-eastern Australia, often found in large numbers feeding on the blossoms of eucalyptus trees. The plant is sweet bursaria (Bursaria spinosa), sometimes called prickly box or blackthorn.
Forensic interpretation of this photograph is complicated. Curiously the right mid-leg of the beetle is detached from the body and hanging precariously from the left hind leg. The long tarsi, or feet, appear to have been partially broken off and the hole in the elytron, or wing cover, made by the thorn appears to be bigger than the maximum diameter of the thorn at its base. This suggests the beetle sustained further damage after it was impaled.
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The thorn penetrates the beetle in the same place as an entomologist would insert a pin, and sometimes a badly placed pin will break off the aforementioned right mid-leg. It would be very difficult to break the elytron in a similar way by manipulating a pin once inserted.
Examples of impalement of other species of scarab beetles on spines or other sharp parts of plants and on barbed wire have been recorded in the literature in Australia, but only rarely.
It is very unlikely that the wind alone could have impaled the elytron. That would be like an insect collector attempting to pin a beetle by throwing it at the pin. The elytron is part of the hard exoskeleton and would almost always deflect the glancing blow of a pin or spine. The chances of impalement through an elytron while in flight would appear to be very remote because the flying beetle holds its elytra open, at a wide angle to the body, and they would hinge back towards the body if touched on the outer side by a spine.
A more likely scenario is that the strong winds blew down a twig or branch to which the beetle was clinging and that the extra momentum of beetle plus branch impaled it. Dislodgement of the fallen plant material at a later date could account for the other damage. Similarly, strong winds might have caused one sweet bursaria branch to thrash against another on which the beetle was clinging.
Ian Faithfull, Extension Support Officer Catchment and Agriculture Services Carrum Downs, Victoria, Australia
鈥� Dung beetles frequently impale themselves on the barbs of wire fences while in full flight. The picture (above right) shows the typical place that barbs catch the insects. I took this picture today, and about 2 metres away another dung beetle had been impaled in the same place. Your picture could be of a bird鈥檚 meat safe.
Toshi Knell, Nowra, New South Wales, Australia
鈥� Actually, this event is quite likely in certain areas. The poor beetle probably did not get there by chance, but rather because it was put there.
In Victoria, the culprit is likely to have been a grey butcher-bird (Cracticus torquatus). These predatory birds, which are about the size of a small dove, eat large insects, small mammals and other birds. They skewer their prey on thorns to hold it while they eat. Sometimes they will impale the prey and leave it for a snack later. Suitable bushes near nesting sites can be festooned with victims, including poultry chicks.
There is a record of a butcher-bird returning to its nest to find its three chicks dead after a spell of cold rain. The bird took them from the nest and hung them in its nearby larder, returning to eat them a few days later.
Shrikes, which are common throughout Eurasia, Africa and North America (and also sometimes known as 鈥渂utcher-birds鈥�, although they are not related) have similar habits.
Rob Robinson, British Trust for Ornithology, Thetford, Norfolk, UK