Soldier Grubs: The Grubs of the Exotic Black Soldier Fly

Natural History

The Black Soldier Fly (Hermetia illucens) has a worldwide distribution in the tropics and warm temperate regions. It is considered a native of the North American continent, and can be found in many parts of the United States. It is exceptionally active in the Southeastern states from April to November. Soldier Grubs are considered beneficial scavengers in nature, and help to digest and recycle decomposing organic material including carrion, manure, fruits, and decaying plant waste. This species can also be found inhabiting beehives. Their association to humanity is limited to compost piles, facilities producing manure, and poorly serviced toilets that contain biosolids. Unlike the common house fly or fruit fly, they are not commonly found in association with humanity (picnics, kitchens, residential buildings, etc.). There is significant potential for use in forensic entomology. The larvae are preyed upon by histerid beetles, sphecid wasps, and certain varieties of birds. Common names include: Privy Flies (associated with outhouses), Meal Maggots (fly fisherman), Soldier Grubs and Phoenix Worms™.

Adult Description


The black soldier fly has a short lived adult stage, normally lasting between 5-8 days. In that time period, their only really function (besides extending the species range) is to find a mate, and oviposit viable eggs in an appropriate food source. This non-feeding stage is so short, the winged adults do not even possess mouth parts, which is the primary reason they are not associated with disease transmission in humans. The blue-black adults range in size from 15-20 mm, and are relatively weak fliers. Breeding of adults occurs in flight; the females can lay up to 900 eggs within their brief lifespan. Because it is an evolutionary mimic, on first glance it can resemble certain varieties of mud wasp.

Egg & Larval Description

The average egg case includes approx. 400-600 eggs; the tiny 1 mm eggs hatch in a little over 100 hours. If environmental conditions are favorable and there is adequate food, the cream colored larvae can reach full maturity in 2-4 weeks. This period may be extended to several months if temperature and nourishment are less than optimal. The tough and leathery chitin-skinned juveniles pass through 6 stages of growth called instars. The last of the instars is distinguishable by a color change from cream to dark gray-brown. The pupae develops within the protective, darker-colored skin of the 6th larval instar, which is referred to as the puparium. Larvae over winter in a sheltered dry location, with pupae development slowing considerably during the coldest months. Depending on a multitude of environmental triggers, pupation occurs irregularly throughout spring and summer, so that the emergence of adults is spread out over an extended time period. There are approx. 2500-2550 mature grubs per pound.

Creative Media

The juvenile form of Hermetia illucens is a robust and beneficial grub that is yellowish in color, dry to the touch, and surprisingly active, as the video illustrates.

High Quality Images