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Popular Science: Even bees guard their nests. Or don’t they?

The first association with the word “bee” is usually a swarm of bees in a hive. We won’t talk about these bees – such as honeybees – here today. Bees of the genus Ceratina guard their nests as well. They are commonly known as carpenter bees, since they build their nests in dead stems or sticks with pith. They are solitary, but just as good pollinators as honeybees, even though they are much smaller – only up to eight millimeters. Compared to honeybees, they are also dark without stripes on the abdomen. And it is these carpenter bees that became an interest of entomologists from our Faculty of Science.
Fig.: Ceratina cucurbitina in her nest; source: original article – Lukáš Janošík

The majority of species from this genus build brood cells separated by partitions. In these brood cells, the bee lays her eggs. Then she settles in front of the outermost cell and guards the nest against potential enemies, until the eggs develop through larvae and pupae into adults. This is precisely the case of Ceratina cucurbitina – these bees are careful mothers. They are also able to crawl through the nest to protect all the offspring directly.

A new strategy has developed in a related bee species: Ceratina chalybea. The majority of bee mothers follow the above described scheme. Some of them, however, plug the nest as soon as they lay eggs, and abandon it probably in order to build a new nest somewhere else. But even the mothers who stay in their nests are not as careful as their relatives, since they lost the ability to crawl through the partitions during their evolution, so they sit at the outermost brood cells, enabling them to be in touch only with the outermost egg.

Carpenter bees are therefore one of the few examples of decreased parental care compared to the ancestor during bees’ evolution. Some species of Ceratina are still eusocial (these bees divide labor in their nest and create castes), which was probably the initial state. Ceratina cucurbitina are solitary mothers taking care of their offspring by themselves. Ceratina chalybea has almost lost parental care completely.

Fig.:  Ruined nests – 1. attacked by predator (probably ants), 2. parasitized by a chalcidoid wasp, 3. occupied by another mother of the same species of bee. Source: original article.

This strategy has of course an important downside: the survival of offspring in an abandoned nest is much less likely. Many of these nests (although plugged) suffer from predation by ants, parasitism by chalcidoid wasps and usurpation by another females of carpenter bees, who discard the eggs of the first female. The benefits of this strategy aren’t quite clear yet. Researchers assume that if C. chalybea build enough nests, at least some eggs could survive, and in the end it equals the reproductive success of more careful mothers.

Carpenter bees have turned out to be a great model for studies of parental care, even more interesting thanks to a reverse process of evolution than expected. Only time and more research can show whether the species of Ceratina chalybea made a huge evolutionary mistake leading to a decrease in the number of offspring in the next generations or adopted a new useful strategy.


Major benefits of guarding behavior in subsocial bees: implications for social evolution; Michael Mikát, Kateřina Černá & Jakub Straka; Ecology and Evolutions; 2016.

Iveta Štolhoferová

Published: May 03, 2017 11:10 AM

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