Black Soldier Fly Larvae (Calciworms) as Food for Reptiles and Amphibians

The larvae of the Black Soldier Fly, Hermetia illucens, have recently attracted a great deal of interest as a food item for herps, birds, fishes and invertebrates. Also sold as “Phoenixworms”, “Calciworms”, “Reptiworms” and “Soldier Grubs”, they are reputed to be superior to other insects in nutritional value. However, much of what has been written about them is confusing and contradictory. Today I’ll review the available research and my own and other’s experiences and attempt to sort fact from fiction, science from opinion.

Nutritional Analysis

There has been some work done on the nutritional value of Black Soldier Fly larvae, and the reports are promising. In fact, a number of zoos now use them regularly.

Most importantly, their Calcium:Phosphorus ratio is approximately 1.5:1 – very close the 2:1 ration that is generally accepted as ideal for most reptiles and amphibians (a poor Calcium:Phosphorus ratio is the main reason that calcium supplementation of crickets is recommended). Also, the actual calcium content of Soldier Fly Larvae is extraordinarily high – up to 8,155ppm as opposed to 20-135ppm in mealworms and crickets.

Protein and fat levels fall midway between those found in other feeder insects – 17.3% and 9.4%, respectively; crickets average 21% protein, while the fat content of super mealworms is 18%.

Word-of-mouth evidence also supports the value of Black Soldier Fly larvae. Bird bone and beak injuries are said to heal faster and certain small frogs may breed more successfully when this high-calcium food item is added to diets.

Antimicrobial Action

Interestingly, over half of the Black Soldier Fly larvae’s fat content is made up of Lauric Acid, which has strong antimicrobial properties and may help to prevent bacterial and other infections.

Size and Use

Soldier Fly larvae are available in 4 sizes, ranging one-eight to three-quarters of an inch in length. Newly-hatched larvae are suitable for Poison Frogs, tiny geckos, spiderlings and such while the largest individuals will be taken by a wide array of herps, spiders, scorpions, birds and fishes.

Other advantages include the fact that they are very active, rarely burrow, and are easily confined to a food bowl.

Rearing and Storing

There is some evidence that Soldier Fly larvae will retain their nutritional value for several months if stored at 50-60 F. Some references suggest refrigeration, but in actuality cold temperatures kill them in short order. I prefer to keep Soldier Fly larvae at room temperature, whereat they will feed readily and be available in various sizes.

Their appetite knows no bounds…a mix of corn meal, cricket pellets, fish flakes and fruit/vegetable trimmings works well. Moisten the food until it sticks together when handled, and spray regularly.

You can also rear the Soldier Flies outdoors by attracting adults to a feeding container, but colonization by a variety of less-desirable insects is likely (please see video below).

Natural History

Over 250,000 species of flies have been described to date. Their diversity of forms and lifestyles is incredible; please see the attached composite photo for an example. Only a small number are harmful to people; most are important decomposers, pollinators and predators of crop pests.

The Black Soldier Fly is proving very useful in farm manure management systems and composting operations (please see below). By consuming organic waste, the larvae limit the food available to Horseflies and other harmful species. They also play an important role in forensic entomology.

Adult Black Soldier Flies are wasp mimics, and most people would hesitate to grab one. However, they are harmless, lacking both stingers and functional mouthparts. Adults live but a few days, dying after mating and egg-deposition.

 

 

Further Reading

Composting with Black Soldier Flies (including kits for home use)

Video: outdoor Soldier Fly breeding system

Rearing Houseflies as Herp Food

Black Soldier Flies mating image referenced from wikipedia and originally posted by Muhammad Mahdi Karim