Got Cats? Get Worms!

Part of the Young Naturalist Awards Curriculum Collection.

by Eric Grade 12, Louisiana - 2005 YNA Winner

When you read my work, you may not think of it as a nature study, but the ultimate purpose of my experiment is to find an environmentally friendly solution to animal wastes. My family has a lot of animals and, specifically, 10 cats. I see the problems with animal wastes daily. The cats live happily in a very large, specially equipped pen. The only problem is that I hate to clean four smelly litter pans. There are no words that adequately express my dislike for this chore. Tired of my complaints, Mom challenged me to design a better system. For years I've observed worms in the compost piles in the woods behind our house. Why not borrow some worms from the woods and have them clean the cat pans for me? Having worms clean up cat mess is my idea of how work should be done.

An adult orange colored cat standing in an outdoor enclosure made of chain link fencing.
One of the cats in Eric's experiment

I knew nothing about vermicomposting and needed to educate myself. I read 12 volumes of Worm Digest,  a few books, and watched a video. I spoke with Dr. TK Carney, a soil and compost specialist with the Louisiana State University Cooperative Extension Service. He discouraged worm-composting cat waste because of the potential pathogens, but he referred me to an expert in vermicomposting, Dr. Rhonda Sherman, with the North Carolina State University Cooperative Extension Service. She did not discourage me, but told me to make certain my cats had no pathogens or chemicals in their systems. She told me to read references on the vermicomposting systems used for reducing pathogens in bio-solid mass from city sewage. Her Web site and its links were the most helpful; they contained information that was more scientific than on many other sites.

It was clear that my experiment would have to be designed in stages; the answers to the first questions would be used to design the next stages. To determine in a scientific manner if a composting cat litter pan was a practical cat pan would ultimately take two years.

The next part of the essay is the scientific method: the basis of my design, my questions, hypotheses, methods, variables, and controls. It's not too interesting to read because it is methodical, but method is necessary to a valid experiment.

Gloved hands holding worms in vermicomposted waste.
The vermicompost

Question: Can a vermicomposting system be a practical alternative to the traditional cat litter pan?
Hypothesis Year 1: Vermicomposting cat wastes will break down the solid waste and reduce the number of pathogens in cat wastes.

I decided that my experiment was workable; I could overcome the problems I had read about. I would have my cats screened for intestinal parasites and fecal pathogens, and take them off flea medications and wormers for four months. I theorized that vermicomposting the wastes of my meat-eating cats would not create the heat problem that manures from grass-eating animals generate. The final product of the vermicomposting cat litter pan would be a beneficial soil amendment for the woods and the landscape around my house.

Boy wearing white gloves sifting through compost.
Working at a vermicompost container

Purpose Year 1, Part 1: To produce a vermicomposting system for cat feces by determining the optimum ratio of carbon to nitrogen for the worms, the ideal food-to-worms ratio, and the ideal end point of the vermicomposting. Part 2: To determine if cats would adapt to the vermicomposting system. Part 3: To determine how to protect the worms from predation by the cats.


Question Year 2: Can a vermicomposting system survive, adapt, and work when antiparasite drugs are used on the cats?
Hypothesis Year 2: A vermicomposting system is a viable alternative to a traditional litter pan if cat predation can be avoided and the worms can adapt to the chemical metabolites of commonly used feline products.

Purpose Year 2, Part I: To test the effects of commonly used feline antiparasitics (antihelminics and insecticides) on a vermicomposting system. Part 2: To introduce the system into a normal home to see if it is practical.Cats are exposed to parasites from the time they are born. External parasites include fleas, ticks, ear mites, and mosquitoes; internal parasites include hookworms, roundworms, tapeworms, and heartworms. It is possible with today's feline products to have a parasite-free cat; contemporary cat owners use a variety of products. The metabolites of these antiparasite products will be passed into the vermicomposting cat pan. To learn about the metabolites of the popular feline products, I read the package inserts and contacted the manufacturing companies.


Boy wearing blue visor working in a lab
In the lab

1. Controlled Variables Years 1 and 2
The following variables are kept as constant as possible in the experimental design.  Environment of worms, Eisenia fetida
a. Containers (10-gallon bins with lids; air and drainage holes drilled)
b. Bedding (soaked peat moss—all systems weighed 20 pounds initially)
c. Moisture (should be "9" on moisture meter)
d. Light
e. Air flow
f. Bedding temperature (regulated with heating pads to a constant temperature of 70° F)
g. Water (tap water from city system)
h. Worm adaptation (Before feeding, allow worms to adjust to new environment for one week; after first feeding, allow one week before taking weight, soil tests, pH, and E. coli counts.)

Boy working at a row of compost bins.
Eric with several vermicompost bins

2. Environment and social structure of cats
a. Housing (normal living area, covered and shaded)
b. Ambient temperature and humidity
c. Diet (Science Diet Adult Dry, regular formula—one cup daily, fed in their normal bowls in their normal place)
d. Water (tap water from city system, provided by a continuous-flow delivery system)
e. Composition of cat "family" (10 cats that have long lived together)
f. People interacting with cat "family" (limited to Eric and Mom)
g. Litter pans (four, each covered with their regular litter—recycled newspaper in pellets)

Two hands holding bucket of compost.
Worms used for vermicomposting

3. Manure worms, Eisenia fetida, all about same size.

4. Carbon source for worms (shredded moist newspaper; slick supplements not used. The shredded paper was moistened with water equal to three times the paper's weight.)

5. Water  (tap water from city system)


Questions Year 1

Experiment A: What is the best ratio of worms to food (cat feces)?
Experiment B: What is the best ratio of nitrogen to carbon in the system?
Experiment C: What is the best feeding frequency for the system?


Method Year 1  (measurements or tests required)

  1. Cat health (parasite level in stool culture when no antiparasite medication is used)
  2. Ambient weather conditions
  3. Weight of cat waste per cat per day
  4. Weight of vermicomposting systems and control bins, weekly 
  5. Worm count and weight (one pound of worms equals 1,000 worms.)
  6. Bedding temperature weekly (adjusted to be the same as ambient temperatures in the house)
  7. Bedding moisture, daily
  8. PH of bedding, weekly
  9. Soil tests of the cat waste, wet newspaper, and peat moss for nitrogen, phosphorus, and potassium content. Then tests of the vermicomposting bins for N, P, and K weekly.
  10. E. coli counts (initially, cat waste, wet newspaper, and peat moss. Then weekly  E. coli  counts of vermicomposting system bins.)
  11. Control bin (set up identically and presented to control cat three times on the first day of experiment; control cat was not treated with any antiparasite medication)


Variables Year 2 

  1. Selamectin (trade name Revolution; made by Phizer), applied topically once to all 10 cats at recommended dose
  2. Leuferon (trade name Program Suspension; Novaritis), given orally once to all 10 cats at recommended dose
  3. Milbemycin (trade name Interceptor Flavor Tabs; Novaritis), given orally once to all 10 cats at recommended dose
  4. Ivomectin (trade name Heartgard Chewables for Cats; Merck), given orally once to all 10 cats at recommended dose
  5. Fipronil Methoprene (trade name Frontline TopSpot Plus; Merial), given topically once to all 10 cats at recommended dose
  6. Imidacloprid (trade name Advantage Topical Solution; Bayer), given topically once to all 10 cats at recommended dose
  7. Fipronil (trade name Frontline Spray; Merial), applied topically once to all 10 cats at recommended dose
  8. Phenothrin Methoprene (trade name Flea & Tick Drops Plus; Hartz), given topically once to all 10 cats at recommended dose
  9. Pyriproxyfen (trade name PreTect; Sergeant's), applied topically once to all 10 cats at recommended dose



Method Year 2

The same measurements were taken of temperature, pH, soil conditions, bin weight, worm count, and coliform count as described for Year 1.

Discussion and Analysis 
The vermicomposting project was divided into five parts and involved two years of observations. In Year 1, I established the optimum conditions for vermicomposting cat wastes with three basic experiments and hundreds of measurements. I found that the most important factors in creating a good environment for the worms were the level of moisture, the amount of aeration, and achieving the proper carbon-to-nitrogen ratio. The worms were able to adapt to slow changes in temperature and pH.

The worms, of course, asked, "What's for dinner?" Since Eisenia fetida manure worms will make use of almost any carbon and nitrogen source as food, the worms were not picky about cat waste. It is a common misconception that worms "eat" waste. The worms get their nutrition from the bacterial, fungal, and protozoal activity in the vermicomposting system. Since the worms have no teeth or digestive enzymes, the microorganisms "predigest" the worm's food and then become food themselves.

Bar chart showing growth of E. Coli colonies over seven weeks across four different groups, including a control group.
Chart 1:  E. coli Colonies in 3 ounces ADP (Click to enlarge)

The end point of the composting was established when the E. coli colony count declined, indicating that the cats' fecal material had been decomposed. Comparison of colony counts was done by counting the number of E. coli colonies from an aliquot sample and then calculating the number of E. coli that would be represented in three ounces of cat waste (the ADP, or "average daily poop").  E. coli counts were taken on the vermicomposting bins on a weekly schedule.

(Coliform bacteria are a group of bacteria that are all of fecal origin and are normal in the intestinal tract but can also be pathological. Escherichia coli is the best-known coliform; Salmonella is probably the best-known coliform pathogen. I established that my cats did not have any pathogenic coliforms by having a diagnostic lab perform a culture on a composite stool sample.)

The E. coli colony count was reduced by 33%, 50%, and 88% by weeks 4, 5, and 7. I had read about municipal human-sewage systems in which 10,000 pounds of worms "ate" 10,000 pounds of sewage sludge in one week, and the coliform reduction was about 50%. The E. coli reduction of 88% in my system exceeded my expectations. It was also noted that the initially acidic system moderated to pH 6-7, and the nitrogen level was high at the end point.

Bare-handed boy reaching through shredded newspaper in compost bin.
Eric working with shredded newspaper

Although worms adjust to changing temperatures, I maintained the system at 70° F, and the worms efficiently composted the feces in just two weeks. The optimum conditions achieved were when the weight of the worms equaled the weight of daily cat feces (ADP); the amount of carbon material present (shredded newspaper) was in a 2:1 ratio to the nitrogen material present (cat feces, or ADP); and daily feeding was performed. (It was awkward in class to continue to refer to cat feces, so I devised the acronym ADP to stand for "average daily poops." ADP doesn't provoke a gag response from the audience.)

Parts 2 and 3 determined whether the cats would adapt to their "special" litter pans. The cats quickly proclaimed that they would use the new bins. They seemed to know the worms were there and dug them out rapidly. Barriers of plastic covers with appropriately placed holes, plastic sheeting, and wire mesh barriers were attempted. A thick layer of ryegrass on top as a barrier to protect the worms, was initially the most successful barrier. With time, however, the cats became proficient in uprooting the ryegrass and engaging in search-and-destroy worm missions. The ryegrass was a protective barrier for the worms when the cats had the box for only 10 minutes. The box was presented multiple times during the day, under close observation. The cats looked forward to the arrival of the bin and were quite curious each time it arrived. They enjoyed getting their paws into the moist and cool peat moss.

Part 4 tested the effects of commonly used feline medications on the vermicomposting system. This part necessitated a "control cat." Mom said no more cats. So Freddie, a young neutered male, was borrowed. He did not socialize with the other cats, and he enjoyed his three visits per day to his vermicomposting pan. I choose the most popular and widely available cat products for testing. After all, the vermicomposting pan has to be practical. I exposed vermicomposting bins to treated cats for about two months (56 days, or eight weeks). Most drug metabolites are eliminated in stools over roughly 30 days. The next month no drug was applied, allowing the worm population to recover and the cats to be totally free of the drug. Then the next medication was applied and tested.

Graph of weekly composting worm counts after treatment of cats with Salamectin.
Chart 2: Selamectin (Revolution) Average Weekly Worm Counts
Graph tracking average E. coli colony count in 3 ounces average daily cat poop.
Chart 3: Selamectin (Revolution) Average  E. coli  Colony Counts


Selamectin (Revolution) is a broad-spectrum antiparasite that kills mites, heartworms, roundworms, fleas, and ticks. Selamectin also kills  Eisenia fetadia  worms. All indicators of vermicomposting system health were affected by Selamectin. Worm counts dropped dramatically;  E. coli  counts rose; and bin weights were less than the control bin. (See Chart 2: Selamectin (Revolution) Average Weekly Worm Counts and Chart 3: Selamectin (Revolution) Average  E. coli  Colony Counts)

Graph of average weekly composting worm counts after treatment of cats with Leuferon.
Chart 4: Leuferon (Program) Average Weekly Worm Counts

Leuferon (Program) is an oral suspension that is given to cats for the control of fleas; it is an insect-development inhibitor and doesn't directly kill fleas. Leuferon was much kinder to the worm population. Worm counts were adversely affected, but to a mild degree. The worm counts also were able to recover starting at the fourth week. The worms were able to compost the ADP as indicated by measurements of worm count, soil testing, pH, bin weight, and reduction in  E. coli.  The control bin still outperformed all 28 Leuferon bins.

Graph of weekly composting worm counts after treatment of cats with Milbemycin.
Chart 5: Milbemycin (Interceptor) Average Weekly Worm Counts

Milbemycin (Interceptor) is an oral tablet that is metabolized in 24 hours, in contrast to the other oral medications in this study. It showed initial declines in worm counts but had less severe adverse effects on the vermicomposting system. (See Chart 5: Milbemycin (Interceptor) Average Weekly Worm Counts)

Graph of average weekly composting worm counts after treatment of cats with Methoprene.
Fipronil + Methoprene Average Weekly Worm Counts

All the other products tested—Fipronil Methoprene, Imidacloprid, Fipronil spray, Phenothrin Methoprene, and Pyriproxyfen—are topical applications. They showed less severe effects on the vermicomposting systems than the Selamectin. All the drugs given to the cats had some effect on the vermicomposting system. It is my opinion that with topical applications, fewer metabolites are eliminated in the cat's stool, and therefore they have less effect on the worms.

Vermicomposting cat wastes completely breaks down the solid fecal material and significantly reduces the bacteria present in a relatively short time. One common cat product, Selamectin, had a profound adverse effect upon the Eisenia fetidia population. Perhaps the best information from my work is that the EPA-approved product Selamectin does have disastrous effects on a sentinel population of invertebrates. Other feline antiparasite products are available which do not have disastrous effects on the worm population.
A simple, effective barrier in the pan that would protect the worms from cat predation was not found in my experiments.

After two years of planning, constructing, experimenting, and observing, I found that the biggest obstacle to testing a practical vermicomposting litter pan was people. My mom was willing to try a vermicomposting pan in the house, but I could find no other volunteer test houses. I had to give the disclaimer that worms will travel out of the bin from time to time. The thought of crawling things in the house made for total negative responses. I guess the average person is just not in touch with nature.
My practical vermicomposting cat litter pan is not a reality, yet. But my cats are enjoying their vermicomposting system, the soil of the landscape around our house is improving, and I'm not cleaning cat litter pans.



Appledorf, Mary. Worms Eat My Garbage. Kalamazoo, MI: Flowerfield Enterprises, 1988.

Mays, Howard. Raising Fishworms with Rabbits. Eagle River, WI: Shields Publication, 1999.

Payne, Binet. The Worm Café. Kalamazoo, MI: Flower Press, 1999.


Boggess, Jay. "The Art of Small-Scale Vermicomposting and Ecotechnology." Worm Digest 1:16, 1997.

Frankel, Stephen. "Some Earthworm Science." Worm Digest 1:7, 1994.

Frankel, Stephen. "What Is Vermicomposting?" Worm Digest 1:1, 1993.

Frankel, Zorba. "Are You a Worm Person?" Worm Digest 1:17, 1998.

Frankel, Zorba. "The Bins We Create." Worm Digest 1:16, 1997.

Parker, Jennifer. "Young Researchers." Worm Digest 1:10, 1995.

Sauvage-Gorman, John. "Red Wigglers in the Privy." Worm Digest 1:8, 1995.

Slocum, Kelly. "Pathogen Reduction in Vermicomposting." Worm Digest 1:23, 1999.

Slocum, Kelly. "The Soil Food Web of Elaine Ingham." Worm Digest 1:18, 1998.

Slocum, Kelly. "Thoughts on System Feeding Rates." Worm Digest 1:23, 1999.

Slocum, Kelly. "Worm Biology 101." Worm Digest 1:5, 1994.

Smith, Kay. "Raising Earthworms with Rabbits." Worm Digest 1:16, 1997.


Hatch, Warren A. Worm Bin Creatures Alive Through a Microscope. Kalamazoo, MI: Flowerfield Enterprises, 1996.


Web sites 
Appelhof, Mary.Worm Composting Resources. Retrieved 10 January 2001 from the World Wide Web.

Red Wigglers. Creekside Gardens, Chehalis, WA. Retrieved 13 January 2001 from the World Wide Web.

Sherman, Rhonda. Worm Publications. April 1997. North Carolina State University, Biological and Agricultural Engineering Dept. Retrieved 14 January 2001 from the World Wide Web.

Worm Digest. Retrieved 13 January 2001 from the World Wide Web. 



Dr. Alma Roy, head of the Louisiana State Diagnostic Lab in Baton Rouge, LA. She showed me laboratory techniques for counting bacterial colonies on MacConkey's agar.
Dr. Rhonda Sherman, at the North Carolina State University Cooperative Extension Service.
I was able to talk with Dr. Rhonda Sherman over the phone. Her Web site, , was very helpful
Novaritis Company. The company sent me pamphlets on their products for cats: Frontline TopSpot, Interceptor, and Sentinel.
Phizer Company. The company sent me pamphlets on Revolution, along with a sample to use.