Life Underwater Series: Life of the Sow bug

Date: June 13, 2019 Author: EcoSpark Categories: Latest

Life of the Sow bug: the aquatic marsupial

The Sow bug is a fascinating benthic macroinvertebrate that will undergo incomplete metamorphosis involving the following phases: the egg, the nymphal stage and the adult stage. Today we will explore the role of sow bugs in their aquatic environments. What does the sow bug prey upon to feed its energy needs? And how does it provide nourishment for its young? To explore these questions, we’ll start at the very beginning-- when sow bug eggs are first laid.

Sow bugs have a unique mating process which involves the male clasping onto the female with specialized appendages (called pleopods) after which they may stay attached for months. During this time, sperm is transferred from the male to the female.  After about 1-10 months, fertilization occurs and the eggs pass into a brood pouch known as a marsupium. This is a water-filled pouch on the underside of the bodies of female sow bugs where the young develop while being protected. In here, the eggs will develop and after incubation the newly developed eggs will hatch and remain in the marsupium for up to a month. Once hatched the sow bugs will go through at least 15 instar phases before reaching maturity. Typically, the lifespan for a sow bug is about 1 year.

Sow Bugs are nature’s scavengers, feeding on dead or injured animals. Some sow bugs have foul-smelling, foul-tasting, defensive chemicals that protect them from the predatory attacks of other species. In our freshwater environments, sow bugs are important because they help to recycle dead and decaying material from the stream bed back into living tissue. 

It is important to note that although they resemble tiny millipedes, sow bugs are actually related to lobsters and crabs as they are part of the crustacean family.

Fun Fact: Sow bugs are the poorest swimmers of all freshwater crustaceans and they can barely swim at all. Their movement is restricted to a slow crawl.

Fun Fact:  There is a myth that says sow bugs are good to eat if you have an upset stomach. Although no one has proven this theory, it has some grounds for potentially being accurate as sow bugs are high in calcium carbonate and this is one of the primary components that makes up their shells.

Interested in learning more about benthic macroinvertebrates and how they can be used to measure the health of rivers and streams? Be sure to follow EcoSpark’s social media to stay updated on our Changing Currents program and our other citizen science and environmental education programs.


Missouri Department of Conservation. (2018). Aquatic Isopod with eggs. Retrieved from:

Carina is an Environmental Education Assistant with the Changing Currents Program at EcoSpark. She is passionate about aquatic ecosystems and educating young minds on the connections between land and water. She recently graduated with a degree in Environmental Studies from York University and a diploma in Ecosystem Management Technology from Sir Sandford’s Fleming College, School of Environmental and Natural Resource Sciences