Everything You Ever Wanted to Know About P. laevis "Dairy Cow"

Do you often wonder about how a certain isopod in your collection happened to originate in the hobby? Have you ever thought about the history of the species? Maybe all you really need is a more in-depth care guide than you can find on the internet, even after combing pages of google searches. In this blog post, I aim to answer these questions and more by providing some insight into one of the most well-known isopods in the hobby, the Porcellio laevis “Dairy Cow.” 

Porcellio laevis  ( also commonly called the swift woodlouse, dairy cow isopod, or smooth slater in Australia) is a species of woodlouse in the genus Porcellio. As the species epithet laevis as well as the vernacular name "swift woodlouse" suggests, the species is capable of quick bursts of speed when provoked. 

This species of isopod is distinctively large, appearing up to 20mm (about 1 in but often larger) long with a smooth dorsal surface. Porcellio laevis has a smooth dorsal surface, which separates it visually from many other species of the Porcellio genus. The males can be identified by their long, spear shaped uropods/ butt spikes. 

It is commonly kept as a pet due to its somewhat easy care requirements and is used quite extensively in the reptile hobby as a cleanup crew in bioactive snake or large lizard enclosures. The species is easy to keep and can be easily established in their chosen enclosure within a few weeks. "Dairy cow isopod" is the commonly used name for this readily available piebald strain of the Porcellio laevis species. The Porcellio laevis was first recorded in Britain in the 13th century but it originated in North Africa. Although identifiable evidence of woodlice is rarely found in archaeological deposits, ‘sub-fossil’ remains of P. laevis were recorded from a medieval infill pit at Stonar in East Kent (Girling, 1979). The processes by which such remains were preserved in an archaeological context are described by Girling, involving the permeation of calcium carbonate into the exoskeleton in hard water, waterlogged conditions. 

 This isopod species has a near worldwide distribution, the species has been found in North and South America, Western Asia, Japan, and some Pacific islands.and has been introduced to Australia, including Norfolk Island and Lord Howe Island.

This species is found under rocks and fallen logs in damp areas and is otherwise rarely encountered. Records from Ireland and Britain also place them in agricultural areas like gardens, farms, and stables where they can be found in dung and compost piles. In the U.S the Porcellio laevis is found extensively on the west coast in states such as California, Oregon, and Washington. 

The way in which the Porcellio laevis births live young is something it has in common with every other terrestrial isopod species and this isopod directly develops from yolky eggs. Both the eggs and juveniles develop within a brood pouch called a marsupium until the first juvenile stage. The use of marsupium is believed to eliminate the need for there to be an external water source for early development since it is filled with fluid from the mother isopod. This is considered some of the most extensive parental care among terrestrial arthropods. 

Porcellio laevis is known to exhibit polymorphism. Sometimes referenced informally as "morphs", multiple polymorphic traits have been line-bred or isolated to produce colonies of Porcellio laevis that can vary widely in color and pattern. The Dairy Cow (or Panda Isopod in Germany) is a perfect example of this. The recessive gene that results in piebald mutation is responsible for the striking pattern and coloration that is so distinctive. The "piebald" form of Porcellio laevis, with its black and white coloration reminiscent of a dairy cow. This piebald form is sometimes referred to as a "dalmatian gene" by those who keep this morph in captivity. It is caused by an absence of pigment in portions of the animal, creating a pattern against the pigmented sections. 

 A cool behavior of these isopods is that Porcellio laevis is one several species of Isopods known to use 'alternating turns' as a defense mechanism, running in a maze-like pattern to confuse or avoid perceived threats. Also observed in Armadillidium vulgare, studies suggest that longer and more frequent exposure to predators causes this species of Isopod to engage in more 'alternating turns' as a learned response 

The Porcellio laevis Dairy Cow has been noted to enjoy substantial amounts of protein and calcium, which is believed to aid in their ability to grow larger than some Porcellio species, and this feeding response has been one of the reasons that so many reptile keepers utilize them to clean up the shed skin, leftover food, and waste in their enclosures. Keep in mind that the nutritional needs of the Porcellio laevis will need to be met or they may go after smaller, softer-skinned inhabitants.  

This leads me to the care guide portion of this video. While a lot of hobbyists keep Dairy Cows for cleanup crews and have them thriving in their bioactive enclosures, there are some of us that keep these animals just as pets. To ensure the health of your colony you will need a well-ventilated container to house your dairy cows. For this most of us use the standard 6 qt Sterlite shoe bin containers from Walmart, Big Lots or Target, though as your colony grows you will likely need to expand to the 15 qt container. You can of course use something bigger or fancier, as you're the one who has to look at your option! Ventilation is key to keeping isopods alive, and I recommend a 1-inch hole covered with screen on each side of the bin for cross flow as well as an extra ventilation hole in the bin lid, if you can, opposite from the moist area.  

You will want to keep your Dairy Cows at a comfortable temperature, which most of us equate to room temperature or roughly 65-90 degrees F or 16-32 degrees C. These are hardy isopods and can survive at temps below and above this range but to avoid a decline in population, I have found that this is a pretty good Goldilocks zone. The humidity for the isopods needs to be above 50% to ensure proper molting but too damp will end in the isopods drowning since they won't be able to completely dry their gills as needed. 

 One important thing to remember is that the isopods will eat their substrate so it should be given some thought. I recommend using an isopod substrate found online in some pet stores or through FB groups, make your own in accordance with recipes found online, or you can always buy Reptisoil or Scott’s brand soil and add nutritional supplementation to that. You will need to add leaves, rotting wood or wood pellets to break down into nutrient dense material if you make your own substrate, but this can be done easily. You will need a wood hide for the dairy cows, because while they like to bury themselves sometimes, you will often see them out and about on the surface.  

You can supplement feed once your colony has grown in size or if they are eating through the leaf litter almost as fast as you replace it. I like to go with high protein fish flakes, I like to use Fluval Black soldier fly formula, since I use it for my fish and aquatic shrimp, I also use brewer's yeast, bee pollen granules, dried minnow and various vegetable scraps including squash, carrots, zucchini and pumpkin. Keep in mind that isopods with lighter color patterns such as the Dairy Cows will often show what they have eaten through their exoskeleton, so if you notice them with a brown or orange tinge, the culprit is usually their food! Finally, make sure you add calcium to the isopods bin, either in the form of cuttlebone, calcium powder without vitamin d, flaked or powdered oyster shell or even limestone. The isopods will utilize it and need it to promote good exoskeleton growth.