You probably don’t want to know this, but wasp mums have remarkable memory

Female digger wasps seem to have far superior memory for scheduling important tasks than I do.

A new study has found that mother wasps can remember the locations of up to 9 of their nests at once and can feed their offspring in age order – picking the nest that contains their eldest in 81% of cases.

The female wasps can even remember the offspring that started out with more food and delay feeding them. This intricate scheduling reduces the chance that their babies will starve.

“Our findings suggest that the miniature brain of an insect is capable of remarkably sophisticated scheduling decisions,” says the lead author of the study, Professor Jeremy Field from the University of Exeter’s Centre for Ecology and Conservation in the UK.

Field is internationally recognised expert in the evolution and ecology of social behaviour, using insect societies as model systems.

“We tend to think that something so small couldn’t do something so complex. In fact, 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.

“As humans, we would achieve this by thinking back to what we have already done, which is called ‘episodic memory’.”

According to the researchers, animals are expected to arrange their activities in time – scheduling – to maximise their ability to survive and pass on their genes to the next generation (fitness).

“Cephalopods and vertebrates with relatively large brains, such as apes and corvids, can achieve this using so-called episodic-like memory, i.e., learning the ‘what,’ ‘where,’ and ‘when’ associated with events,” they write.

Field says: “We don’t yet know how wasps achieve these remarkable mental feats.”

Field and his collaborators studied wild female digger wasps (Ammophila pubescens) which dig short burrows in the sands of England’s heathlands.

After finding and paralysing a caterpillar, the female digger wasp puts her prey in the burrow and lays an egg on it. She covers up the entrance with a protective plug of small stones and soil and heads off, to start a new burrow or to feed her existing offspring.

If the larva hatches as planned, it has a convenient meal nearby to sustain it until mother returns days later.

When the mother returns, first, she checks to see if the larva has survived. Then she brings it as many as 8 more caterpillar snacks over the course of up to 7 days.

Finally, she permanently closes the nest and moves on, leaving her offspring to pupate and eventually emerge as an adult wasp.

“Despite nesting in relatively featureless bare sand, often among hundreds of intermingled nests of other females, mothers rarely make errors in revisiting their nests,” says Field.

“Only 1.5% of the 1,293 food deliveries in the study went to other females’ nests.”

When the researchers replaced the nest seal plugs with ones made by other female digger wasps, they found that the “females always relocated their nests and did not hesitate or behave unusually.”

This suggests the mothers do not identify their nests by the odour or appearance of the nest seals. Instead, the researchers suggest that “nest relocation at least partly involves learning the positions of landmarks relative to nest entrances.”

The researchers also tested what happened when they changed  the caterpillars as the mothers prepared their burrows. They found that female wasps given larger caterpillars adjusted their schedule to wait longer before providing additional food and stared new burrows during the delay.

If a female wasp found that the offspring next in line for a snack had died, either due to a developmental failure or parasites, she quickly replaced it with a new egg and caterpillar and shuffled the nest to the back of the feeding queue.

Mothers did sometimes make mistakes, especially if they had more offspring or when the feeding order was altered due to a death.

“Memory capacity is often thought to be ‘expensive’; the brain needs the machinery – in the form of neurons – to remember, and the energy to carry out that function,” says Field.

“Lots of experiments have been done in labs, for example putting insects in mazes and other tests to find rewards.

“But this study shows what the wasps really do in the wild – it reveals why this ability is relevant to their lives, and why natural selection has favoured this.”

The research is published in the journal Current Biology.