>In response to the amount of caffeine in used coffee grounds.  41 mg of caffeine per 17 gm of used coffee grounds.

According to this study, bees are attracted to nectars with caffeine at very low levels and may be repelled at higher levels. Used coffee seems like it has concentrations too high to be attracting bees wanting caffeine. Another study on ants indicated that bees are attracted to the aroma of coffee. In that study, they were looking for an attractant they could as poisonous ant bait.  It may be that the bees are just attracted to the coffee aroma and not the presence of caffeine in the grounds.  

>Caffeine is bitter tasting to mammals and is both toxic (24) and repellent to honeybees at high concentrations (25, 26). If bees can detect
caffeine, they might learn to avoid flowers offering nectar containing it (27). We found that honeybees were deterred from drinking sucrose solutions
containing caffeine at concentrations greater than 1 mM (Fig. 4); they also have neurons that detect caffeine in sensilla on their mouthparts (fig. S3).
However, nectar concentrations did not exceed 0.3 mM (0.058 mg/ml), even though levels of caffeine in vegetative and seed tissues of Coffea
have been reported to be as great as 24 mg/ml (28). This implies that pollinators drive selection toward concentrations of caffeine that are not
repellent but still pharmacologically active. 


>Caffeine in Floral Nectar Enhances a Pollinator’s Memory of Reward
G. A. Wright, et al. 


Bill Hesbach
Cheshire CT

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