The all-consuming nature of motherhood in the wild

Everyone loves videos of baby giraffes wobbling on fresh legs beside their tall, gangly mother. We all coo to see baby sea otters curled up on their moms’ floating bellies and smile at fuzzy emperor penguin babies tucked between their mothers’ legs.

Here in Colorado, mother black bears, mountain lions, and mule deer birth delightfully cute babies. However, not all motherhood in the animal kingdom is so warm and fuzzy.

In the wild, animal mothers face various threats to themselves and their growing offspring, pushing many species to unique and sometimes grotesque approaches to motherhood. One particularly intriguing mothering strategy called matriphagy involves self-sacrifice and is found in various types of spiders, fish, and other insects.

Many human mothers undergo a massive identity shift after becoming mothers for the first time. It’s common for new mothers to feel absorbed by their new identity. They have to learn how to balance the needs of their children with their own.

A European spider that has made residence in North America in the last 100 years, including right here in Colorado, hasn’t quite figured out that balance. The black lace-weaver spider is one of the species of spiders that regularly exhibit matriphagy, which is the consumption of the mother by her offspring.

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Found commonly in or near man-made structures, the black lace weaver female lays a sack of eggs in the summer. She guards it carefully until the spiderlings emerge a few weeks later. A few days after they emerge, she feeds them trophic eggs, or unfertilized eggs produced for the sole purpose of feeding living young.

Three to four days after that, the young molt and the mother start exhibiting jumping and drumming behaviors on the web. The movements are a form of communication to her progeny that it is time for them to eat their mother alive. Within a matter of hours, the young swarm the mother and devour her alive.

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Six different families of spiders exhibit this bizarre approach to motherhood known as matriphagy. Why have black lace-weavers and other animals evolved this behavior? In an experiment by the Department of Entomology at the University of Wisconsin Madison, scientists removed the mother black lace-weaver from the environment before the spiderlings’ first molt, and spiderlings suffered significant consequences to their growth, behavior, and likelihood of survival.

These spider kiddos were much smaller in size, had a lower survival rate, were more likely to lack the skills to successfully capture prey, and were more likely to kill their siblings for a food source. For all of these reasons, the mother’s all-consuming sacrifice seems to be a crucial part of her offspring’s survival.

At the end of the day, no matter their approach, all animal mothers share the goal of ensuring the survival of future generations of their species and they may resort to extreme measures to do so. Remember, this Mother’s Day, all types of moms make enormous sacrifices for their children, so thank a mom today.

Savanna Henning is a Foley Graduate Fellow and Educator at Walking Mountains. She spends most of her time outside, helping K-8 students learn from the natural world.