Answer: Yes

Most of us love making a hot cup of coffee in the mornings, but could we be using our coffee grounds as a repellent?

Summary of Our Scientific Research

There is no solid evidence of coffee grounds being able to repel mosquitoes, but during the Zika virus outbreak in 2016, some websites claimed coffee grounds as the best option(1).  However, there is some evidence of burnt coffee grounds, along with caffeine, inhibiting the growth of mosquito larvae(2).

Be careful though, as mosquito larvae could potentially benefit from the introduction of coffee grounds.(3)

The reason coffee grounds are able to inhibit larvae growth is the caffeine it introduces.  Caffeine has different effects depending on the insect it is introduced to. For mosquitoes, caffeine prevents mosquitoes from swimming up to the surface, killing them before they can become adults(4).

Our Thoughts

Rubbing coffee grounds over your skin won’t hurt, but it won’t help either.  But if you can track down the location of where the mosquitoes are breeding, you can at least delay the growth of future pests, if not outright killing them.

Being able to control the population is a step up from letting a mosquito infestation happen, but be warned that the study only tested coffee grounds with the mosquito species Aedes aegypti.  Also, another study claimed that coffee grounds could act as nutrition for some larvae(3).  If you don’t know the type of mosquito that’s around your house, you may not want to risk it, especially if your area is in dire need of a good repellent.

How to Use Coffee Grounds 

Once you’re done making that sweet cup of coffee, take the burnt coffee grounds to the area of mosquito larvae.  It’s up to you whether you use recently-used coffee grounds or week-old coffee grounds(some sites say to use one or the other).  Once spread around, the larvae will either stop developing or get a free meal. It’s a risky move, but one worth taking.

If you only have a minor mosquito problem and can’t be bothered to spend money on a couple of pesky mosquitoes, then using your coffee grounds won’t hurt.  However, you’ll need to know where the larvae are, and locating larvae can be pretty difficult.  

Or, you could just pour coffee grounds into every source of water you have, hoping to catch the larvae.  I don’t recommend it, but you could!

Sources

1 – miaminewtimes.com –  “There’s one other way to ward off the pests: Use good ol’ café cubano. In the video above, Abuela Mami,a local company that ships care packages of Cuban treats to your door, shows you how to combat mosquitoes by using coffee grounds.”

2 – scielo.br –  “Caffeine and used coffee grounds completely blocked the development of Aedes aegypti in the early stages, in treatments with the concentrations 1.0 mg/mL and 50 mg/mL, respectively. More advanced stages and even adults were obtained in lower concentrations of both substances, enabling observations to be made of mortality rate, longevity and esterase patterns.”

3 – snopes.com –  “However, the survivorship of larvae for UCG 0.01 and UCG 0.05 in comparison to the controls suggested that in nutrient-poor systems, UCG in low concentrations could benefit the larvae and boost their survivorship and hence, increase the number of larvae that successfully hatch into adults. Small amounts of UCG could enhance bacterial and algal growth, thus providing food for mosquito larvae.”

4 – johnnybpestcontrol.com –  “For example, larval mosquitoes that are exposed to caffeine will lose their ability to swim up toward the water’s surface upon maturing into adulthood.”

Other Household Items as Mosquito Repellents

Checkout our analysis of other household items as natural mosquito repellents: