Not just poo on the menu: Say hello to the snail-killing dung beetle
Anyone would be forgiven for assuming that dung beetles feed on, well, just dung. The truth is rather more complex, as new and striking findings on a South American species illustrate.
Canthon chalybaeus, as it turns out, is an aggressive predator of the snail Bulimulus apodemetes — the first time dung beetle predation on a non-arthropod has ever been recorded.
This certainly seems an odd choice for a diversion into active carnivory, given that firstly and most obviously, snails have a formidable natural defence in the form of a shell. Then, this particular species is much bigger than the beetle. Also throw in the fact that dung beetles lack the mandibles (sharp insect ‘teeth’, if you like) which lend themselves to such endeavours, and you’ve got to say top marks for ambition in the face of seemingly moderate prospects.
Predators have been noted before
Across the around 7,000 dung beetle species, it would be fair to say that the general meal preference list would go something like dung, dead things, live things. Predation is not their natural game, but some have evolved to be more than up for giving it a go. With around another 1,000 still to be described, yet more with aggressive tendencies may become public knowledge.
Cases of dung beetles taking on ants and millipedes have been reported before, with the weapons of choice being essentially serrated parts of their face, which in the case of ant attacks ends with the prey being decapitated. This neatly underlines the insect world’s unerring commitment to both weirdness and ultraviolence, if it were needed.
Where live millipedes are preyed upon, research has shown a marked preference for targeting the injured or dying to kill off and eat, which makes sense in terms of energy expenditure-to-nutritional content. Snails are notably slower-movers with far less manoeuvrability than millipedes, but there’s still that hard barrier to overcome, and from what’s been observed so far, C. chalybaeus targets healthy B. apodemetes individuals. Breaking new ground, as well as shells.
Notes on a killing
So, this is how it’s done: C. chalybaeus climbs onto the snail’s shell and remains motionless for up to 25 minutes. If the snail fails to remove it with twists and turns, the attack begins using serrated facial and leg features, increasing in intensity until the snail partially withdraws into the shell and ultimately dies within a few minutes.
The researchers who described this behaviour also found that the beetles release eight compounds during the attacks, including acids and toxins, with them speculating that these, too, could play a significant role in the ultimate demise of the unsuspecting gastropod.
Then, it’s time to bury the evidence, and break the shell to remove the soft body. It’s worth noting that snail attacks were found to be more the business of males of the species, due to the fact that after removal, the quarry is then served up as a nuptial ‘gift’ to potential females, attracted by pheromone secretions. And who said that romance is dead?
Chance encounters mean snail peril
As with all the dung beetle predatory behaviours recorded to date, these encounters with snails are opportunistic. Less active searching like ground beetles or playing the ambush predator like mantids; more along the lines of ‘if it happens, it happens’.
All in all, a fascinating new insight into members of a group of the most well-known beetles. A broader trend may well have been spotted, and the scientists reporting this phenomenon for the first time suggest that further investigation is merited among related species. Snails, whose soft bodies are favoured food by many animals, may be facing even more existential threat than previously imagined.