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For those of you who, while drinking your morning cup of Joe, have asked yourselves, “I wonder how bugs respond to caffeine?” then you are in luck, as science has you covered. Although it may sound strange, several studies have been conducted concerning the effect that caffeine has on insect and spider species. As it happens, caffeine can have a variety of effects depending on the arthropod species ingesting the substance.

When caffeine is contained within its natural plant form, caffeine works like a natural pesticide, as it causes an herbivorous insects’ nervous system to stop producing essential enzymes. When these enzymes are inhibited in an insect, paralysis and eventual death result. Not all insect species will die as a result of caffeine consumption, as some insects only experience lasting reproductive problems. What is particularly strange, are the odd behaviors exhibited by some insects following caffeine consumption. 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. Spiders who were fed caffeine-laced flies also exhibited strange behaviors when it came to web-spinning. A now somewhat famous research study found that caffeine intoxicated spiders became unable to form symmetrical webs as a result of ingesting caffeine.

According to James Nathanson at the Harvard Medical School, many plants contain caffeine in order to ward off damaging insect pests. This ability on the part of plants is an evolutionary adaptation that works quite well at ensuring a plant’s survival in a world where insect pests are abundant. In fact, many entrepreneurs are hoping to develop caffeine-based pesticides. 

While caffeine-based insecticides may seem promising, not all scientists are believers in its effectiveness at killing problematic bugs. According to Bussey Professor of Biology, Carroll M. Williams, caffeine can only kill a wide variety of insects provided that they are exposed to a large quantity of the stimulant substance. At the end of the day, caffeine is not a particularly powerful or even effective substance for killing insects. However, a recent study showed that when caffeine is added to known insecticides, a much smaller amount of insecticide is required for killing bugs. This means that caffeine makes known insecticides more potent. By making caffeine an ingredient in insecticides, much less insecticide is needed, which could save money while benefiting the environment.

Have you ever seen a fly land in a cup of coffee?