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Ideas | Mark Peters

It’s only human to see our own sins in animals

ap/globe staff illustration

“Klepto,” derived from a Greek word for a thief, has been a part of English words for some time. We’ve talked about kleptocracies and kleptomaniacs since the 1800s. But thievery isn’t limited to the human race, at least in the wild world of science. A recent study of mollusks resulted in the coining of a new term: “kleptopredation.” That’s when a predator waits until the belly of its prey is full before striking.

It’s hard not to anthropomorphize when discussing animal behavior — from stealing to slavery. The natural world is complicated, and metaphors are useful in communicating the simple ideas behind complex behaviors. But it is problematic too, because it forces biologists to affix moral judgements on other organisms.

Kleptopredation, for instance, is far from the first term to lump animals with human criminals. Scientists have been discussing “kleptobiosis” since at least 1901. As William Morton Wheeler wrote in his 1928 book “The Social Insects: Their Origin and Evolution,” “certain small but aggressive species, which secure at least a portion of their sustenance by waylaying the foraging workers of another species and snatching away their prey, deserve the name of brigands (cleptobiosis).” I’m not sure if “brigand” is more insulting to ants or humans, but the comparison seems apt.


“Kleptoparasitism” has been observed since at least the mid-20th century and involves similar thievery. A 1994 issue of Nature defines the term in a description of seabirds: “At sea, skuas obtain food mainly by ‘kleptoparasitism,’ meaning that they search for smaller seabirds that have caught food, chase them, and force them to drop or regurgitate the food.” Another kleptoparasite is the cuckoo bee, who takes after the cuckoo bird. While the birds lay eggs in other species’ nests, the bees invade and colonize other bees’ hives. Such behavior has inspired additional forms such as “kleptoparasitic” and “kleptoparasitize.”

These terms are the predecessors of “kleptopredation,” which invokes a specific sense of predation: one critter consuming another, at least partially. In a recent issue of Biology Letters, Trevor J. Willis and other researchers coined this new word to discuss a type of predatory banditry, as they observed sea slugs (called nudibranchs) devouring hydroid polyps after the polyps chowed down on zooplankton. So the sea slugs get a two-for-one meal. In human terms, it would be as if a person left a holiday meal, only to be killed and eaten by Hannibal Lecter on the way home.


Thievery is just one concept used by scientists to describe behavior that has a strong similarity to human behavior. Ants in particular have inspired a lexicon of fascinating terms used by entomologists to describe extremely complicated behaviors. In a phone interview, Stephen Pratt, who studies how insect societies are organized and how they act as a collective intelligence, discussed a variety of terms used to describe insect behavior, explaining the “tension between the value of the metaphors and the risks of the metaphors.”

That tension is found in ants described as armies and farmers, but it’s particularly high when it comes to so-called “slave-makers,” a term first found in Charles Darwin’s revolutionary “On the Origin of Species” in 1859. Pratt described how these ants form “raiding colonies” that attack similar species, and they do a lot worse than steal meals: “they steal the brood — the larvae — and raise them up as workers.”

The term “slave-maker” has understandably drawn criticism over the years. Pratt said some feel the term “trivializes human slavery — or brings an unwelcome moral cast to what ants do.” Technical terms for the slave-makers — “dulosis” and “social parasitism” — exist, but don’t have the same communicative power, which is a concern even in dry scientific articles. Pratt said, “Even when we’re writing formally, we’re trying to write something compelling. We want to get the attention of the public.”


Even scientists who are strongly opposed to anthropomorphism sometimes find it useful.

Amanda Ridley, a behavioral ecologist working on animal behavior, said by e-mail that she usually tries to avoid anthropomorphism, because: “it affects what we can conclude, how we fit it into the theoretical framework and compare it with other empirical findings, and we also stand vulnerable to criticism from scientific peers if we anthropomorphize.” But Ridley also notes, “For media statements I am more likely to anthropomorphize to avoid scientific jargon that may alienate some readers of my work.”

Animal behaviorists can’t escape the specter of human behavior, and whether they should even try is an open question to be answered on a case-by-case basis. As Pratt put it, anthropomorphic terms are useful “if they convey some very precise meaning.” Sometimes that precise meaning involves the human animal too.

Mark Peters is the Ideas language writer.