Nematodes for Fleas – Effective Flea Control For Your Garden

If you have ever had to fight a flea infestation, you will probably know how difficult it is to sometimes get on top of the situation, especially if the problem is not identified at an early stage. Over the last couple years, I have had hundreds of queries from people (with or without pets) that just can’t seem to win the battle against fleas, even though they have treated their home multiple times. Their mistake is usually ignoring (or just not knowing) that fleas can often thrive outside, reinfecting pets and increasing their numbers over time. This article will cover using beneficial nematodes for getting rid of fleas outside your home, and it is a powerful, non-toxic and safe way to find relief without breaking the bank.

What are beneficial nematodes?

Nematodes are microscopic non-segmented worms (sometimes called “roundworms”) that seek out an insect host (either in the developmental phase or even adults) to feed and reproduce. If the thought of putting these tiny worms in your garden terrifies you, just remember that your soil already has lots of them (if that makes you feel any better lol). The term “beneficial” nematodes is an important differentiation, as some nematodes (such as the “root knot” species) can damage the vegetation in your yard, whereas the beneficial ones will “help” in some way or another (hence their name).

The three that are highly effective for getting rid of various grubs in your yard have the scientific names of “Heterorhabditis Bacteriophora Nematodes (HB)”, “Steinernema Carpocapse Nematodes (SC)” and “Steinernema Feltiae Nematodes (SF)”. However, it is unlikely that you will need to remember those names, as the product containing nematodes will usually mention what insect(s) it targets on the packaging.

Do all beneficial nematodes kill fleas and how do they work?

While it is possible for any beneficial nematode to have varying success on garden pests, only the “Steinernema Carpocapsae” species are highly specialized flea killers, and as such, I highly recommend that you make extra sure your product contains them (or at a high percentage).

After applying them to your yard (more on this later), the “Steinernema Carpocapsae” nematode will hunt down fleas in their pupae, larval, juvenile and even adult stage, enter their bodies and release deadly symbiotic bacteria that will kill them in less than 48 hours. It doesn’t stop there, however, as these nematodes will use the flea’s body juices to multiply and their young will repeat the cycle, seeking out more fleas in your yard. It is worth noting that the nematodes don’t actually “eat” the insect, the bacteria released destroys its victim and fleas will never become immune to it’s killing power.

Many people are concerned about the millions of worms, all invisible to the human eye, somehow patrolling their yard for all eternity. However, although the first part is correct, once all the reachable fleas (in all stages of their life cycle) or other harmful insects are defeated, they will merely starve (after six weeks) and biodegrade.

Are nematodes harmful to humans or pets?

No, beneficial nematodes are entirely safe for your family and pets. The United States Environmental Protection Agency (EPA) has determined that nematodes are exempt from federal registration. They have been classified as “macro-organisms” (instead of micro-organisms like viruses, etc.) and are safe to use without restrictions (Vol. 47, Fed. Reg. 23928, 1982). Please do not be scared of using nematodes for fleas; you can even use these little guys on veggie gardens without any cause for concern.

Remember, if you use these nematodes for flea control, you are not introducing something new into your yard. There are already potentially millions in your garden soil, and you are merely increasing their number so that they can effectively deal with the flea infestation. This means that you can continue to use your garden as you usually do, so don’t put off that barbecue or pool party, thinking that these microscopic worms will somehow infect someone or pose any danger.

Ironically, while I fully understand the need for it sometimes, using various chemicals (which people seem more comfortable with) to get rid of the fleas will pose a potential risk for your pets and people who live with you. In most cases, you would be advised to keep your pets indoors for awhile whereas this is not the case when using beneficial nematodes, yet another reason to seriously consider using them instead.

If nematodes kill fleas, are they dangerous to useful insects?

According to Koppenhofer (who is a leading expert on this subject), the answer is no. In fact, in all the studies performed, beneficial insects (such as ladybugs, etc.) are immune to nematodes. I also spent a good couple hours researching this question to ensure it’s accuracy (it a widespread concern from my readers) and came to the same conclusion; beneficial nematodes will not harm useful insects in your yard, making them an excellent solution to kill fleas without repercussions.

In addition to these findings, the same research shows that nematodes won’t have an adverse effect on other garden life, such as birds, squirrels, and household pets (as mentioned above), so there really shouldn’t be anything holding you back from using them for your outdoor flea problems.

How long does it take for beneficial nematodes to work?

Once the nematodes have been applied to your yard (more on this later), they will need to seek out and find fleas to infect with their deadly bacteria. Once they locate these little pests, they will need at least 48 hours before moving on, and even though you will have millions of these little assassins, I recommend that you set your expectation for around two weeks for the nematodes to make a noticeable dent in your flea population.

During this process, you will not find dead fleas lying around like you may expect with a chemical treatment, as their bodies are being broken down by the bacteria, leaving your garden completely free of pests, both living and otherwise. I love this, even though the fleas would eventually biodegrade over time, this speeds up the process significantly.

A couple warnings and best practices before using nematodes

I thought I would squeeze this last section in here before going through the application process and if you are still reading this, you are a rockstar! Here are a few things to keep in mind before you decide to use nematodes:

1. It is important that you purchase the beneficial nematodes from a reputable seller that hasn’t kept them in storage for too long because these living, macro-organisms can die. In fact, even if purchased from a trustworthy company (such as Arbico Organics), you ideally need to put them in the fridge (not the freezer) after purchase and use them within two weeks maximum. I recommend using them immediately, as you don’t know how long they have been with the supplier.
2. If you live in an area where you have freezing temperatures (daily) during the winter, rather leave the treatment for the beginning of spring, as the nematodes won’t be able to function correctly under very cold conditions (in most cases). It is also worth noting that fleas are dormant in freezing temperatures, so that is yet another reason to wait until the warmer weather hits.
3. The best time to release your nematodes is in the late afternoon or early morning when the temperatures are nice and cool. Yes, these flea killing ninjas don’t like freezing weather conditions, but they also don’t like the heat of the midday sun lol. I suppose they are a little fussy like that, but take my advice and follow these instructions and your nematodes will perform like rock stars.
4. If the nematodes have a fishy smell when you open the sealed enclosure, it is likely that they (or at least a portion of them) have died. This goes back to point number 1; it is critical that you find a well-reviewed seller, as dead nematodes are not going to be too much help with your flea infestation. 😉 It might help asking the supplier (beforehand) if they will accept a return if this happens to you.
5. While it won’t be harmful or dangerous to your health, I don’t recommend that you use nematodes for indoor flea control. If you are having flea problems in your home, I recommend a combination of DE powder and a few homemade flea traps. Using both (at the same time) has proven effective for thousands of my readers, so I highly recommend that you give them both a try.

How to apply beneficial nematodes for fleas on your lawn (or anywhere in your garden)

Step 1: After you have found a good place to buy nematodes, purchase enough to cover the area that you want to treat for fleas. As a general rule of thumb, you will need about 5 million flea eating nematodes to cover around 1500 square feet. If you get a little too much, it will only produce quicker results (within reason of course) so don’t be too afraid of this step.

Step 2: Depending on the brand of nematodes, your purchase may include a spray bottle that can be attached to a hosepipe. If that is the case, it is as easy as clipping it on and using it around your yard/garden. It will also take care of ensuring that the area is properly soaked, which is an important part of making sure the treatment works. A little tip, I recommend that you add 1-2 drops of food coloring in the spray bottle so that you know when the solution is all finished. You can also skip the next step.

Step 3: If your beneficial nematodes didn’t come with a hosepipe spray canister, you could easily use a regular watering can (preferably a large one). Before adding the nematodes to the water to create your flea killing solution, ask yourself how many refills you will need to gently “wet” to all the necessary areas. If that answer is “5”, then divide your nematode supply by 5, place one of them into your watering container, use it and after it’s finished, repeat the process with the next part, etc. Before you start, however, it is essential to use a hosepipe to soak the entire area (yard/garden), as the nematodes won’t work if they don’t have a moist environment. If you have garden sprinklers (and you are sure they will reach all the areas), just leave them on for about 15 minutes.

Step 4: If you live in a very dry environment, I recommend that you water the entire area every three days for up to around two weeks. This will make sure that your precious nematodes don’t die and have all the moisture they need to find the fleas and get rid of them for you. As mentioned before, doing this during early hours or late in the afternoon will yield the best results.

How do you prevent the fleas from coming back to your yard?

In reality, you can repeat this application as many times as you want (budget permitting), but unless you have a significant flea problem that continuously rises it’s ugly head, apply the nematodes every four months. While not required, this will ensure that your outdoor areas remain flea free, which is especially important if you often have wild animals or other people’s pets invading your garden from time to time.

Another cool tip (which I plan to cover in a separate article) is using cedar wood chips to repel fleas from your yard. While not perfect, if you use enough, they are a fairly decent way to control fleas outdoors. Give them a try in conjunction with these nematodes, as it is fairly cheap and look quite attractive in most gardens (at least I think so). Make sure that you put a decent quantity on your perimeter fence areas if you think that fleas may be hopping across from a neighbor’s yard. 😉

In summary, using beneficial nematodes for outdoor flea control is an extremely effective and affordable solution. They are safe and won’t even hurt useful insects in your garden. It is also worth noting that they are very easy to apply, and shouldn’t take you more than 1-2 hours to cover a fairly large area (even quicker if you have the hosepipe canister). I hope that you found this article useful and if you want to support my blog, please share this page on social media. If you have any questions, leave me a comment below.

Natasha Anderson

Hello! My name is Natasha, and I have been helping people with their insect problems since 2012. I have published a book, worked with many pest control companies, and helped thousands with various infestations on a one-to-one basis. My goal for this blog is to create evidence-based guides that are easy to understand, provide sufficient depth and can be trusted to be very accurate. Please remember that my guides are for informational purposes only, and that you agree to the terms of use when reading content on this website. If you leave a comment, I typically respond within 48 hours.