Class - Insecta
Order - Diptera
Family - Mycetophilidae, Sciaridae
Size:  2 mm

The term fungus gnat (figs. 57 & 58) generally applies to members of two closely related families of flies, Mycetophilidae and Sciaridae.  They are mosquito-like in appearance with feathery antennae, but tend to be much smaller.  Their overall color is almost black.  The larval stage (fig. 58) develops in damp, decaying matter, usually containing fungal mycelia.  Most infestations in homes come from the high organic matter soil of potted plants.  However, some may develop in other areas of fungal growth such as mushrooms.  Fungus gnats are almost universally present in any situation where rich substrate is used, either for growing scarab larvae or for potted plants.  It is the adult flies rather than the larvae which are the main nuisance, especially when they emerge in large numbers from substrate.  The tiny, elongated worm-like larvae have a characteristic, black head capsule (fig 59).  Like the beetle larvae, they feed primarily on bits of decayed plant matter such as decomposing wood and leaves, are not necessarily indicative of poor sanitation, and are not known to pose any threat to scarab larvae.  Sticky fly tapes hung from the ceiling around your rearing area will help trap many of the adult gnats.  These tiny flies primarily become a problem in rearing containers after scarab larvae have progressed to the pupal phase of their development, and the substrate is no longer being disturbed on a regular basis.  These pests are basically innocuous as compared to those discussed previously.
 

. Fig. 48:  A close up of the larva of a fungus gnat.  Note the small, black, hardened head capsule which is typical of this family of flies.

Class - Insecta
Order - Diptera
Family - Drosophilidae
Size:  2-3 mm

Tiny fruit flies, also known as pomace flies or vinegar flies, are present outdoors during warm weather.  These flies, which belong to the genus Drosophila (fig. 49), also may be pests in and around the house.  Fruit flies breed in overripe and rotting fruits and vegetables, and other wet, decaying plant material.  They are able to complete a life cycle in only 10 to 12 days.  Fruit flies particularly are a household problem during the fall when they enter houses to escape cooler outside temperatures.  Although they can become a nuisance on fruit in scarab enclosures in cases of poor sanitation, they are basically harmless.  Fruit flies can easily be confused with the far more dreaded phorid flies, which they closely resemble in size and shape.

Phylum - Nematoda
Size:  usually under 10 mm

Soil nematodes ( figs 61 & 62) are tiny, elongate, free living roundworms that are common in soils and composts everywhere, from the freezing Arctic to dry, hot deserts.  They are particularly abundant in grassland ecosystems.  To give you an idea of exactly how common these nematodes are, consider this: one cubic foot of soil can contain millions.  Many species feed on small bits of decaying organic matter, and like the larvae of fungus gnats, can become very numerous in scarab rearing substrate.  They are free living and are not known to pose any threat to scarab larvae, though they can reproduce VERY rapidly and compete with the larvae for food.  In particular, they will invade pellets of dry dog food, causing it to decompose faster and generally making it less attractive to scarab larvae as food.  Frequent changing of the substrate can help keep their numbers under control.