A new study shows that a mother digger wasp (Ammophila pubescens) can remember the locations and feeding history of up to nine nests at once. These tiny insects have a brain smaller than a pinhead, yet they are somehow capable of managing a highly complex parenting routine that rivals human-level organization.
Despite their small size and simple brains, these wasps are strategic about making decisions, like delaying food for a larva that’s already had enough, or replacing a lost offspring, and adjusting their whole schedule accordingly. This remarkable cognitive ability could change how scientists think about memory, planning, and the mental capabilities of organisms with tiny brains.
“They can remember where and when they have fed their young, and what they fed them, in a way that would be taxing even to human brains,” Jeremy Field, first author of the study and a professor at the University of Exeter, said.
It is already known that animals with large and complex brains, like octopuses, apes, and humans, use a type of memory known as episodic memory to recall the what, when, and where of specific past events. This allows them to mentally revisit personal experiences. However, how do mother wasps manage to perform similarly complex tasks with such tiny brains?
Mother wasps rarely made a mistake
The study focused on a population of Ammophila pubescens, a species of solitary digger wasp that lives in the sandy heathlands of southern England. Female wasps of this species build short underground nests, one for each of their offspring.
The process begins with the mother digging a burrow and then paralyzing a caterpillar, which she places inside as food. After laying an egg on the caterpillar, she covers the nest with sand and small stones and heads off to begin another nest or continue caring for the ones she has already started.
What fascinated scientists was what happened next. A few days later, the mother would return to check if her larva was still alive. If so, she would bring it more food, sometimes as many as eight caterpillars in total, over the next several days. Once feeding was complete, the nest would be permanently sealed, and the mother would never return.
This seems straightforward until you consider that a single female may be managing up to nine active nests at once, all scattered across a sandy area, surrounded by hundreds of other nearly identical burrows created by different wasps.
“Despite nesting in relatively featureless bare sand, often among hundreds of intermingled nests of other females, mothers rarely make errors in revisiting their nests. Only 1.5% of the 1,293 food deliveries in the study went to other females’ nests,” Field said.
But how was a wasp able to recognize her nests among so many?
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Managing the nests and a hectic feeding schedule
The researchers discovered that the wasps weren’t identifying nests based on smell or visual differences in the entrance plugs, since swapping these didn’t throw them off. Instead, they appeared to use memory of landmarks like nearby stones or patterns in the sand to recognize the location of each of their nests. However, it wasn’t just the spatial memory that impressed the scientists.
The wasps also showed signs of remembering what had happened at each nest. They almost always visited the oldest offspring first, feeding them in age order in over 80% of cases. If a larva had received a particularly large caterpillar during an earlier visit, the mother would delay its next meal, shifting her focus to younger offspring that hadn’t had as much food.
When researchers intentionally swapped the caterpillars to make it seem like some larvae had received more or less than they really had, the mothers adjusted their plans accordingly. In some cases, when a larva might die before the mother returns, the mother would replace it with a new egg and caterpillar, but wouldn’t treat it like the others.
Instead, she would move that nest to the back of the feeding queue, ensuring that her time and energy were spent first on those more likely to survive. However, some mistakes did occur, especially when the wasps had more nests to manage or when the feeding schedule had to be rearranged.
Still, the overall success of their scheduling was astonishing given the simplicity of their brains.
“We tend to think that something so small couldn’t do something so complex. However, our findings suggest that the miniature brain of an insect is capable of remarkably sophisticated scheduling decisions,” Field added.
This finding has also given rise to many questions, for instance, how exactly do the wasps store and process the memories related to the nests and larval feeding? Do they have an insect version of episodic memory, or are they using some other mechanism entirely? Also, can similar abilities be found in other solitary insects?
Hopefully, further research will reveal the answers to these intriguing questions.
The study is published in the journal Current Biology.
