Even if you think your parents played favorites among you and your siblings, they probably weren't as blatant as a wasp mother. Unless maybe they put your sister in a locked, secure room and fed you to mountain lions. To be fair, a queen paper wasp (Polistes chinensis antennalis) is a single mom with a lot on her plate. She sets off alone in the spring, after mating, to found a new colony. She mixes her spit with plant fibers to make a pulp that she shapes into a house of delicate, hexagonal rooms. Then she lays her eggs in the cells and waits. Eventually her eggs hatch into helpless larvae. Later, those larvae spin cocoons to seal themselves inside their cells while they metamorphose into adults. The developing young are vulnerable whenever their mother flies off to find more food. Neighboring wasp queens like to visit an unguarded nest, snatch a baby from its cell, and bring it home to carve up and feed to their own young. To give her own pupae more protection, the queen may heap extra pulp on top of their cocoons. This slows down the looters who would hack into a cocoon while a queen is away. But it takes time and effort to make the pulp for these defensive barriers, so queens don't build them on every cell. Sho Furuichi and Eiiti Kasuya, of Japan's Kyushu University, studied 47 paper wasp nests in the wild to find out more about how queens defend their young. First the researchers photographed each nest and measured how much of each cocoon's surface (if any) was covered by defensive pulp. They continued photographing the nests each day so that they could monitor which cells held larvae or cocoons. Just 13 of the colonies survived long enough for the new adult wasps to emerge from their cells; the researchers only used the data from these nests in their analysis. Separately, to learn more about predation, the researchers interfered with 10 wasp nests. They removed the queens and plucked out the eggs and larvae, leaving only the pupae in their (guarded or unguarded) cocoons. Then they used videocameras to record what happened when predators visited the nest over the next week and a half. Queens build larger barriers on the cells of their most mature offspring, Furuichi and Kasuya discovered. The first larvae to spin their cocoons, getting ready to transition to adulthood, are the best-defended by their moms. The larvae that make cocoons later on get smaller barriers. Or these late bloomers may get no barrier at all. This makes sense, the authors say, because the most advanced young are also the most valuable to their mothers. The sooner new adults emerge from those cells, the sooner the queen can have a real colony up and running. The nest is most vulnerable while the queen is managing it alone. So the young that are closest to being able to help out are her favorites. If some of the less mature ones get snatched and eaten by predators in the meantime, oh well. The videos of queen-less nests showed that bigger pulp barriers did keep the young wasps safer. "Predators totally avoid the cell with large pulp structure on the cocoon," Furuichi says. Instead, attacking wasps opt for easier targets. Nest building hasn't gotten as much attention from researchers as other kinds of parental care, Furuichi and Kasuya write. But clearly wasp queens are flexible about how they build their nests, changing their strategies based on how their young are maturing. When thinking about how animal parents choose to spend energy (or not) on their offspring, we shouldn't forget about the structures they build. We should probably also never hire a wasp as a nursery architect.
Image: by John Wattie (via Flickr)
Furuichi, S., & Kasuya, E. (2015). Construction of Nest Defensive Structure According to Offspring Value and Its Effect on Predator's Attack Decision in Paper Wasps Ethology DOI: 10.1111/eth.12374