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Some Like it Hot: Sick House Flies Purposely Induce a Fever

house fly

Fevers are thoroughly unpleasant and usually accompanied by other troublesome physical symptoms. Even so, they are often a good sign that our immune system is kicking in to help us “fight off” a nasty infection. Outside the world of endotherms (those of us that regulate our own body temperatures), some ectotherms—those that must seek heat to keep warm—also make use of fevers by finding a heat source to purposely induce them, a phenomenon known as a behavioral fever.

You might wonder why any creature, great or small, would choose to have a fever. One possible reason may be remarkably similar to the reason for fevers in humans: they help fight infections. If you weren’t aware of the massive insect-fungi war taking place right under our noses, the Cornell University Mushroom Blog says it all. In short, fungi have a terrible habit of infecting and killing all kinds of insects, and the insects’ best weapon of defense is to run to the warmest place possible. Make no mistake: the fever is not fun for the flies, and there are health risks and costs (like elevated metabolism and possible organ failure) the longer the fever is maintained. Nevertheless, it’s their best option.

In a recently published PLOS ONE paper, aptly titled “Discriminating Fever Behavior in House Flies, researchers at Penn State investigated this phenomenon further by testing whether house flies self-induced a behavioral fever in a dose-responsive manner to fungal infection. Fungus-infected flies were placed in boxes with temperature gradients (ranging from 77 to a balmy 102 degrees Fahrenheit), and their behavior was monitored throughout the course of the day.

Early in the morning, when the fungus had been actively growing all night, the flies hung out longer in the warmest parts of the box. As the flies’ increased body temperatures began to inhibit fungal growth, the flies would move to cooler areas; however, at night, the fungus would again begin to grow unabated, and the cycle would repeat. Interestingly, it was found that the higher the fungal dose, the higher the temperature of the induced fever. The researchers acknowledge that more work needs to be done, and other factors may contribute to the flies’ preference for heat. Nonetheless, this study underlines the importance and effectiveness of temperature regulation for suppressing infection in a surprising variety of species.

Citation: Anderson RD, Blanford S, Jenkins NE, Thomas MB (2013) Discriminating Fever Behavior in House Flies. PLoS ONE 8(4): e62269. doi:10.1371/journal.pone.0062269

Image Credit: Public domain

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