I read that spreading de will cause fleas to dehydrate will salt do the same thing or no?
Greetings! Thanks for the great question.
The short answer is no, salt won’t dehydrate fleas like DE.
Salt for Flea Control
Only a handful of reliable sources mention using salt for flea control. All this literature is from the early 1900’s, well before modern insecticides were developed. Additionally, these papers and books don’t talk about using salt within homes. They recommend covering the ground of animal shelters (hogs, horses, poultry, etc) with a layer of salt. Then water is sprayed on the soil to dissolve the salt. Sea water also works. While drying, it desiccates (dehydrates) the immature fleas (larvae and eggs). This method is also done outside around homes, and sometimes in dirt-floor basements. However, thoroughly wetting down carpets is a bad idea, as it will lead to mold.
Even if this method was used on carpeting, it may not work. The larvae live at the base of carpet fibers. They are protected by the carpet canopy. The carpeting creates its own micro-environment where temperature and humidity are regulated. The addition of salt will probably not alter these conditions much, unfortunately.
I’ve read accounts online of salt being used for flea control. However, these claims are unfounded with no supporting evidence. It may work, but it’s highly speculative. I believe these webmasters are just writing articles which they know people are looking for, whether or not they are true. I’ve seen a video on YouTube of a guy killing adult fleas in a bowl with salt. However, adults aren’t the life stage to target, as they only make up 1-5% of the total infestation. The immature stages must be killed to end an infestation.
Bishopp, F. C. 1921. Fleas and their control. Farmers’ Bulletin 897, United States
Department of Agriculture, Washington, D.C., 16 pp.
Ewing, H. E. 1929. A manual of external parasites. Charles C. Thomas, Baltimore,
Maryland, 225 pp.
Gray HF. Destructive and Useful Insects—Their Habits and Control. American Journal of Public Health and the Nations Health. 1951;41(11 Pt 1):1428-1429.
Hinkle, N. C., Rust, M. K. & Reierson, D. A. Biorational Approaches to Flea (Siphonaptera: Pulicidae) Suppression: Present and Future. Journal of Agricultural Entomology 14, 309–321 (1997).
Combating fleas. Don Carlos Mote.  p. October 1930
Salt vs. Diatomaceous Earth
Salt doesn’t have the same desiccating properties as DE. Their structures are completely different. Salt has a crystalline structure. While DE used for insect control is more of a powder (amorphous silica). Crystalline silica, the DE used for pool filters, doesn’t work for insect control. High temperatures cause amorphous silica to turn into crystalline silica (particles of glass). As a result, it loses its absorptive powers.
Amorphous silica works through a few different mechanisms. Its microscopic edges are razor-like and cut open an insect’s cuticle (exoskeleton), as a result its liquids drain out. However, more importantly, DE is highly absorptive of oil. DE contacting an insect will suck up the wax covering its body. Without this coating of wax, they can’t retain water, and they’ll desiccate over time. The more absorptive the DE is, the better it’ll work.
The best DE products for insect control are highly pure amorphous silica, and have a uniformly small particle size. They should contain very little clay and less than 1% crystalline silica. The diatomite should be properly milled. The diatoms should be well-separated and physically intact if possible. Look for food-grade diatomaceous earth.
One final note: Diatomaceous earth has a lot of buzz around it regarding its effectiveness for flea control. People are drawn to “natural” control methods. However, there are few scientific studies which demonstrate its efficacy. It may or may not work to end an infestation.
Hope this helps!