Normally coroners and homicide investigators will not have any call to rear blow flies or flesh flies. The forensic entomologist does that. But I have dealt with coroners who at least harbored the idea that their offices could eventually do everything for themselves, without the aid of a professional. The following section therefore has a triple function: First, to outline what I do personally when rearing flies for hire; second, to make it clear just what is involved in such activities, so that would-be fly culturists can better judge of what they would hope to attempt; and third, to serve as a protocol for serious entomologists who would set up for themselves.

The first requirement to rear blow flies or any other arthropods is an area in which you can precisely control temperature, humidity, and day length. For maggots temperature is by far the most important of these variables. One of the most convenient ways of regulating the rearing environment is to have a small room set aside for this task, with a separate heating and air conditioning system. A second way is to use an environmental chamber. These methods are not mutually exclusive. Here at I my lab facility I use both.

My rearing room is about eight feet long by ten feet wide by ten feet high. This room is sealed off from the rest of my lab with an air-tight door, and is ventilated by an air-conditioning unit I built into the outside wall. There are no windows. In addition to the air conditioning, the room has its own separate heating system, controlled with a separate thermostat. It is lighted by a fluorescent ceiling unit. This unit is controlled by a built-in wall timer, which is programmable in units of 15 minutes. That is, if I want I can set the unit to give any combination of light and dark, as for example, to go off for 2 hours and 45 minutes, come on for 15 minutes, and then go off again (I would never actually use this combination). As the air conditioner depresses the humidity in the room, when I am rearing flies I run a large floor humidifier most of the time.

This system has only one disadvantage: as even the space in a small room is quite large compared to a humidifier, to keep the humidity at a decent level (say 60%) you have to refill the storage tank constantly, or use several smaller misters as auxiliaries. Fortunately, as I will show below, relative humidity is not so important for rearing maggots as for rearing some other arthropods, as the former normally live in a damp medium, and are reared in containers with restricted air-flow. However, a high and constant humidity allows one to accurately judge how often to moisten the containers, and represents one less variable about which to worry. The use of an environmental chamber helps one keep the humidity at a steady, adequate level. I have three chambers, two of one type and one of another.

I have two Biotronette environmental chambers like the one pictured above. These were designed for general biological lab work, and work fine for rearing insects like blow flies. These chambers allow me to set temperature above ambient. This is accomplished by use of ceramic heaters, screwed into light sockets along the top of the inside. These heaters are connected to a thermostat. Unlike the room heating, however, they are also connected to a timer, which, with the lights, can be set to come on and off whenever I like. Each chamber is also equipped with a small fan that runs continually. I have used these chambers for most of my fly rearing.

In spite of their utility, these chambers have three disadvantages. First, they work best in a cool room; as they have no refrigeration system to depress temperature if it gets too hot. Second, they do not come with an integrated system for raising humidity levels: You must add this yourself. I currently use a small, portable "cool mist" humidifier inside the chamber. The model I use is equipped with an "humidistat," or built-in rheostat. This rheostat allows me to set the humidity over a range of levels. In the photo of the chamber the humidifier can be seen at bottom left. Third, because of the potential variability of both temperature and humidity, these must be monitored by use of a thermohygrometer that will keep track of and display minimum and maximum values. A digital variety of one of these thermohygrometers is shown in the photograph above. I have about ten of these units, and use them to keep tabs on conditions in all my work with live arthropods.

My third environmental chamber is pictured to the right. It is a HotPack Model 317332-M. As you can see from the door jam at the left of the photo, this is a huge chamber, that I had to install permanently in my lab, along with a water softener, a reverse osmosis (RO) machine, and a deionizer (DI). The humidifying system, which is built-in, uses the water these supply. This system allows the humidity to be controlled within +/- 2%. Because humidity is very sensitive to drafts, the chamber has double doors. The inner door is glass, and can be left closed for a cursory examination of the contents.

Temperature control for this chamber is also extremely precise; it can be set from 0-70 degrees C, and once set, will not vary more than +/- 0.5 degrees C. This precision is very convenient, as it both eliminates unwanted environmental variation and frees up the investigator from tedious recording duties.

Temperature, lighting, and humidity can also be "stepped" through a "ramp and soak" program to give different values at different times of the day. Such a chamber is essential for determining Accumulated Degree Hours. It is also ideal for rearing flies in casework.

Now for a word about the settings I use. This depends a lot on the conditions under which the maggots developed prior to my receiving them. If they initially developed on the cool side, say at about 20 degrees C, then I would try to use that temperature to complete their development, and the same would be true if I suspected they developed at 30 degrees C or higher. If on the other hand I thought they originally developed at a variety of temperatures, I would probably try to rear them at more middling temperatures, say at 23 degrees C or 25 degrees C, as most of the studies on ADH have been done in this range. Whatever the temperature, I would try to keep the humidity high and constant. I usually shoot for about 60%.

I find it easiest to rear maggots communally until they pupate. I keep the maggots from each collection together. For example, if I collect two groups of maggots, one from around the mouth of the corpse and one from a wound on the leg, I put all the maggots from the mouth area together in one container and all the maggots from the leg together in another one.

The containers are set up as follows. I fill the bottom one inch of a wide-mouthed plastic container with damp sand. A large number of these wide-mouthed chambers are shown on the lower shelf of the chamber in the above photo. These plastic chambers were designed to rear insects, mainly mosquitoes. They are ideal for our use because they have wide top that allows easy access for cleaning and to look for pupae.

Once the sand is in the jar, I set a wide plastic bottle top upside-down on top of it, to prevent soiling from the raw meat that I put in next. Beef liver works well and is very inexpensive. But I prefer beef that has been cut into small sections for fondue. Needless to say, this costs much more, but the size is very convenient. One or more of the fondue sections can be added as needed. Over and around this meat I place a crumpled section of moist paper towel. Then I add the maggots, and screw-on the top. The tops, by the way, contain a small piece of coffee filter, that has been cut to size and wedged under the window screen they came with. These pieces of filter are necessary to retain the smallest maggots and to prevent tinier flies like phorids (coffin flies) from escaping. The electrical tape around the seam serves the same purpose. Both filters and tape are clearly visible in the photo.

I then examine the jars every day, usually in the morning. I replace the damp towels when either they become dry, or become soiled with blood, etc. This usually happens every day or two. I also examine the chambers daily for puparia. I remove these first puparia and place each one in a separate plastic vial with a label. This label includes the collection site, the date and time the puparium was found, and the color of the puparial cuticle. This color varies with age. It is white shortly after molting, and turns dark brown, almost black, over the next 12 hours or so.

After I've spotted the first puparium, I then examine the jar more frequently, every hour or two if possible, until most of the maggots have pupated. I treat these subsequent pupae in the same way as I did the first.

This usually leaves me with tens and perhaps hundreds of plastic vials, each containing a single puparium with a label. I treat these much as I originally treated the maggots. I look every morning to see if any have emerged. When the first one or two come out I add a second label, giving the day and time of their emergence. I then examine the vials every hour or two, and treat the remaining flies as I treated the first few.

Before removing the flies for pinning I leave them alive in the vial for a few days, to give them time to harden their exoskeleton. Then I kill them in a killing jar and examine them under a microscope, to determine if they all belong to the same species. They usually do but there is no guarantee that they will. I have had cases where there were several types of maggots on the body. It stands to reason that occasionally some of these mixed lots would produce two species of adults. After confirming the identification of the dead flies I then fix a chart showing the dates and times for pupation and emergence.

Next, I select 20-30 flies to pin and label for permanent reference. I use #3 pins, and pin the fly over the puparium from which it emerged, much as one would pin a predacious insect over its prey. The "cap" of the puparium is often detached, and occasionally in two pieces. In these instances I use clear fingernail polish to glue the cap to the sides of the puparium once it is on the pin. I finish by printing a tiny label containing all the relevant information, using print 4-6 points in size. These labels are printed on 100% rag paper with a laser printer. The pinned flies are then stored in standard fashion. The remaining, unpinned flies are stored in a freezer until there is no longer a chance that they will be needed.