Some Helpful Hints and Tips to get your Flies through the Cold

Introduction

Fruit Flies (Drosophila sp.) are one of the most popular feeder insects for those animals that require smaller prey items, such as poison dart frogs. Unfortunately, these typically easy to culture insects often encounter difficulties with colder weather. This blog entry will address the most common issues, and what to do about them.

Shipping

The reduced temperatures winter brings makes shipping live animals even more difficult than it already is, and shipping fruit flies are no exception. At Josh’s Frogs, we ship using styrofoam lined boxes and with heat packs when the temperature drops, but even so, the interior temperature of a package can vary widely in transit, depending on how it is handled by the carrier, and the length of it’s travels.

During winter, Josh’s Frogs ships using styrofoam lined boxes with heat packs.

In a styrofoam lined box, a fruit fly culture will maintain interior temperatures approximately 10 degrees above that of it’s surroundings. Adding a heat pack will raise the temperatures another 10 degrees. Even at 20 degrees above ambient temperature, the cultures will experience a wide range of temperatures in transit, due to the change in the daytime highs and overnight lows the part of the country the package passes through experiences. This constant temperature shift certainly does not have a positive effect on the fruit fly cultures – at best, it has a neutral effect, and often negatively impacts the culture. It’s very easy for cold weather to slow down or stop the natural progression of a fruit fly culture during shipping. Often, it delays peak production by several days – that is why producing cultures sometimes take a few days to catch up after shipping in winter. If the fruit fly culture is exposed to very cold temperatures, flies, pupae, and/or larvae may perish. Once situated in a proper environment the culture will rebound, but sometimes chilly weather may cause the culture to fail, and/or allow grain mites to exponentially reproduce in the culture, leading to it’s demise.

Temperature

Average house temperature during the winter is substantially less across the United States. Lower temperatures will not necessarily result in less fruit flies produced per culture, but can greatly increase the length of time it takes a culture to produce flies. Accompanying the delay in fly production is an increased threat of grain mites – these pests are capable of reproducing in a much wider range of conditions than fruit flies are. Grain mites are present in all fruit fly cultures, and in most situations are not harmful, but if given the proper conditions, they are capable of overrunning a fruit fly culture, and eventually crashing it. Typically, if the temperature is increased to a level more favorable for fruit flies, they will resume production, and the mites themselves will be out competed.

There are several ways to insure that fruit flies receive the required temperatures during the winter (ideally as close to 78F as possible). The easiest method is to keep the fruit flies near a heat source, such as a water heater or lights used to light the animal enclosures. When trying this, remember that heat rises, and often cultures located nearer the ceiling of a room will be several degrees warmer than ones located near the floor. Alternatively, creating an incubator of sorts for the cultures can keep them warm. Anything from reptile egg incubators to a plastic container with a heat source, such as a basking bulb or heat pad, can be effective.

Humidity

The cold winter weather generally leads to the furnace running most of the time. This not only increases the household temperature, but also substantially decreases the relative humidity. Ideally, fruit fly cultures are maintained at 60-80% humidity, and lower humidity can result in the culture media drying out, allowing a ‘skin’ to form over the surface of the media (just like pudding can form a ‘skin’ if left in the fridge). This ‘skin’ will suffocate the larvae, or cause them to climb up the sides of the culture in search of oxygen. Spraying the culture with a bit of water will correct this issue.

Under ideal humidity, fruit fly pupae should be concentrated around the mid level of a culture.

By looking at the placement of pupae on the side of a culture, you can infer if the culture is receiving the proper humidity or not. Under ideal conditions, the pupae will be spread evenly throughout the sides of the culture, with most of them located at mid level. If most of the pupae are located at the top of the culture, the humidity is too high. If the pupae seem concentrated lower in the culture, towards the media, the humidity is too low. Keeping cultures in plastic storage drawers, such as those made by Sterilite, is a quick and easy way to insure that proper humidity is maintained.

Conclusion

Winter poses many challenges to the proper production of fruit flies. Using the hints and tips outlined in this blog post, most problems can be solved quickly, and plenty of fruit flies can be produced for your herps.

One of the most common variables overlooked in culturing fruit flies is the surface area used. I have seen cultures with everything under the sun used as surface area. The two most common sources of surface area in fruit fly cultures are coffee filters or excelsior. Each has their pros and cons.

For best results, coffee filters need to be folded so they look like pie slices. I will fold 5-6 together and push the point into the media. Coffee filters will absorb excess moisture in the culture media and therefore act as a moisture barrier, so they are less likely to dry out or become soupy. The downside to coffee filters is that they can get too wet and will collapse and bury the fruit fly media and hurt production.

Excelsior has been a long time staple in fruit fly cultures. It creates tons of surface area and takes less time to use (just grab a handful and throw it in the culture). The downside is that is quite messy to use as some of the fibers will inevitably fall out with the flies when feeding.

All cultures sold at Josh’s Frogs will be setup with excelsior.