Spices as Fly Deterrents

Flies spread diseases when they land on food. People from cultures in hot climates where flies are abundant and bacteria grow quickly tend to use a lot of spices; the explanation is that spices inhibit microbe growth so people develop a preference for spicy food because they are less likely to get sick.  The goal of this experiment was to determine whether flies prefer meat without spices. In Experiment 1, unseasoned and seasoned pieces of beef (n=8/group) were placed outside for 4 hours, then 48 hours later the number of larvae were counted. Beef with garlic had fewer larvae than unseasoned beef while beef with cayenne pepper had no larvae (H=15.09, p<0.05). In Experiment 2, ten fly eggs (Musca domestica) were placed on beef seasoned with garlic or cayenne pepper versus unseasoned beef. Seasoning had no significant effect on the proportion of larvae that hatched (p>0.05); thus, spices cause avoidance of egg laying rather than inhibition of egg hatching. In Experiment 3, flies were placed in a container with four 45 gram ground beef balls containing 0, 1, 2 or 3 grams of cayenne pepper. Seven of 10 flies demonstrated a preference for the unseasoned beef and three showed a preference for the beef with 1 gram of cayenne pepper. In conclusion, flies prefer unseasoned meat for laying eggs and feeding. If flies avoid seasoned meat, then there is reduced opportunity for fly-borne disease; this may be an alternative explanation for why spicy foods are preferred by people in hot climates where flies are abundant.