Dung beetles are humble insects. They feed on the faeces of other mammals. In many species, a male dung beetle flies to a fresh pile of dung, shapes a piece of it into a ball, and quickly rolls it away from the pile so others don’t grab it.
Reputedly, male dung beetles have rolled dung balls a thousand-times heavier than their own body weight. The researchers found that given a choice, the dung beetle Onthophagus orpheus strongly preferred dog poop. This was in line with other studies that have shown dung beetles prefer the faeces of omnivorous mammals to that of herbivores, like cows. In the laboratory, the dung beetle made larger brood balls on dog poop than cow dung. Male offspring developed in larger brood balls than female offspring, suggesting more resources are provisioned to the sons. And this sex difference was more pronounced with cow dung than with dog dung. O. orpheus eggs also developed faster in dog poop and the progeny that emerged were larger. However, egg mortality was also higher in dog poop. Why the mortality was higher with dog poop remains unclear. One possibility is that pets are routinely administered antiparasitic medications and they accumulate in faeces, and they could have increased the mortality of the larvae and the pupae of dung‐dwelling insects. The insect cannot be faulted for its unfortunate mismatch. It is our lack of foresight. D.P. Kasbekar is a retired scientist.
On August 12, a team from Clark University in Massachusetts, U.S., reported in Ecology and Evolution that these dung beetles are vulnerable to a previously unforeseen risk: dogs.
The researchers inferred that “the dung type most strongly preferred by adults was also associated with the lowest offspring survival”, creating a mismatch between preference and performance. They added that this “suggests that accumulation of domestic dog waste … may pose a widespread but underappreciated risk to urban dung beetles”.
A female will inspect the ball and decide if it is good enough to lay her egg in. If it is, the couple mate, the female lays her egg, and the ball is then buried in a tunnel in the soil. The ball will provision food for the offspring. Dung beetles quickly clear dung piles and recycle soil nutrients. Plants benefit, too: the seeds that pass through a mammal’s gut get planted deep underground, in dung-fertilised spots.
Dung beetles have been known to increase plant growth by 17%.
