This method doesn’t involve the dark, prepupal larvae which are self-harvesting
The coffee colored black soldier fly grubs (prepupae) are the final stage before pupation into adult BSF (Hermetia illucens). To our advantage they are programmed by nature to crawl away from the food source in search of a suitable pupation site. In a properly designed BSF unit these larvae crawl up a ramp and drop into a collection bucket where they will live for weeks without any maintenance.
The method described below is for harvesting the earlier stages when the larvae are actively feeding and growing. It doesn’t work for the mature larvae because they don’t eat therefore aren’t attracted to the bait in the collection container. It works very well for the light colored immature larvae.
The Immature Larvae Collection Device or ILCD (old butter tub)
Take a cheap container and cut some small holes around the bottom edge.
(click on images to enlarge)
Add something delicious (any food scraps will do), and simply place it on the surface of the compost. I used moistened fish food because I’m training my fish to eat it and this is a good way to introduce them to the flavor (I feed the larvae to the fish). Just about anything will work, but fresher items will make handling the collected larvae more pleasant.
The photo below was taken 2 minutes after placing the tub on top of the compost.
This is after 11 minutes.
The photo below was taken 40 minutes after adding the container.
This quick harvest totaled about 2 cups (.5 litre) of small to medium larvae. I don’t have many large larvae at this time due to the crash I caused in the colony a few weeks back. I do have a lot of larvae, just not large ones yet.