Natural vs. Synthetic Fly Spray: What Works Better?

There’s this pervasive idea that natural products are less effective than “chemical” products. 

Side note, here… EVERYTHING is a chemical. Water is a chemical. Plants are made of chemicals. “Chemical free” is a marketing tactic. That’s a whole blog post for another day. Anyway…

This concept, in my opinion, is most dangerous around our animals - and in this case, at the barn. We’ve been trained to believe that in order for something to work, it has to have “the bad stuff” in it. That it’s a necessary evil to have to use carcinogens, endocrine disruptors and neurotoxins to get the job done (keep the flies away from our horses).

Ironically, synthetic repellents are actually less effective than plant-based repellents. If you’re new to the natural wellness scene, that might seem untrue. But if you’ve been here, that shouldn’t come as a surprise.

 

THE DANGERS OF PYRETHROIDS

Let’s break this down. The active ingredient in (most) fly sprays fall into the Pyrethroid family. This is the synthetic version of natural Pyrethrins found in Chrysanthemums. Most often, you’ll see them in the form of Permethrins. And these are inherently dangerous because they are quite literally designed to target and damage the nervous system. 

They’re technically safe to use on mammals in low concentrations. But… fly season lasts for 6 months, from late Spring to early Fall. Fly Spray doesn't actually build up in the mammalian nervous system - metabolic pathways clear synthetic pyrethroids pretty quickly. That’s still 6 months, about 360 sprays if you’re spraying twice a day, of neurotoxin application. Directly to your horse’s largest organ, the skin.

I’ll preface this part with: these reactions are not a given. We don’t believe in fear-mongering. Most horses will be fine. But it’s important that we’re fully informed about the products we’re using on them - they count on us to make these kinds of decisions on their behalf.

Pyrethroids have been known to cause acute toxicity in horses, with symptoms ranging from muscle tremors and excessive salivation to seizures, difficulty breathing and in very rare cases, death. More common, less serious side effects are topical, most often presenting as hives and itching. Severe side effects are mostly the result of off-label and excessive use. But, just as with humans, some horses can be hypersensitive to what others tolerate well.

RESISTANCE: SYNTHETIC VS. NATURAL

The mode of action that makes Pyrethroids initially effective is also the reason that flies can easily develop resistance. We know that flies reproduce very rapidly - so they can “evolve” rapidly. This comes in the form of target-site mutations, a genetic change that alters the shape of a specific location within the cell, preventing the pyrethroid (or other chemical) from attaching to the new site shape. Heavy exposure speeds up this already very quick process.

It is much harder for flies to develop a resistance against plant-based fly sprays. This is for a few reasons: natural fly sprays like ours utilize multiple active compounds, they don’t have specific target sites, and they break down really quickly (so the flies have less exposure and therefore less opportunity to mutate).

Most “chemical” fly sprays have 1 or 2 active ingredients. Natural fly sprays typically include several active ingredients (plant extracts). Our Fly Spray has 8. The more complex a formula is, the harder it is to evolve against - it’s much simpler for a fly to develop 1-2 mutations than it is to develop 8.

Synthetic sprays typically target one specific receptor or enzyme in the fly nervous system… so it has one mode of attack. Plant extracts attack several systems at once, so they can simultaneously cause things like cell membrane disruption, breathing, and digestion. This broad-spectrum approach allows for a more complete attack.

OVERALL

I built this brand on the premise that nature can solve natural-born problems better than human-built solutions can. Is that always the case? I can’t say that definitively - my area of expertise specifically sits in the animal wellness industry. But it intuitively makes sense that plants can repel pests better than humans can repel pests. And the modes of action explained above, as well as a significant amount of data, do support that.

At the end of the day, it’s about choosing products that we feel good about using. I didn’t feel good about using Pyrethroids, on my horse or near myself. Some may be - and that’s okay. I created this option for those who aren’t.

SOURCES

Bao W, Liu B, Simonsen DW, Lehmler H. Association Between Exposure to Pyrethroid Insecticides and Risk of All-Cause and Cause-Specific Mortality in the General US Adult Population. JAMA Intern Med. 2020;180(3):367–374. doi:10.1001/jamainternmed.2019.6019

Scott JG. Evolution of resistance to pyrethroid insecticides in Musca domestica. Pest Manag Sci. 2017;73(4):716-722. doi:10.1002/ps.4328

Vijverberg HP, van den Bercken J. Annotation. Action of pyrethroid insecticides on the vertebrate nervous system. Neuropathol Appl Neurobiol. 1982;8(6):421-440. doi:10.1111/j.1365-2990.1982.tb00311.x