You are here:

Entomology (Study of Bugs)/Co-Incident Insect in Soldier Fly Larvae Compsoter


QUESTION: Hi Ed, Thank you so much for volunteering your time, it is an enviable service.  I have a 'bio reactor' of Black Soldier fly larvae that I add food scraps too.  The larvae eat the food scraps, then upon reaching sufficient size to pupate (about 3 weeks time), the pre-pupae crawl out of the bioreactor where I capture them.  I then place them in a Pupation box where they turn into flys, mate and lay eggs.  I then collect the eggs to produce more Black soldier fly larvae.
These unidentified insects showed up in my bioreactor and in my pupation box.  
I ASSUME they are feeding on food scraps in the bioreactor.  
I KNOW they are feeding on the Black Solider Flys (The flys, not the larvae).  I observe when the flys emerge from their shells that the unidenifited insects will latch on to the fly's legs and between the segments on the fly's abdomen.  They assume a postion like an aphid on a plant.  
I am guessing that I will not be able to prevent them from being in the bioreactor, but I have not observed them to attach to any black solider fly larvae, so it may not be an issue.  So I am looking for ways to prevent them from becoming an issue in the pupation box.  The two strategies that I have considered are:
1 - Change out the pupation box frequently to prevent a colony of the unidentified insect from establishing a large population
2 - Treat the pre-pupae before adding them to the pupation box.  The pre-pupae (and larva) are very durable and may be able to withstand conditions that the unidentified insect cannot.  Treatments could be... submersion in salt water, acidic water, alkaline water, oil, detergent... I have not tested any of these yet.

Can you help me identify these insects, and can you suggest some possible treatments I can trial.

In the pictures, you can see the insects are dark/red colored.  I believe that these are full grown adults.  I also observe clear colored and smaller versions of this insect in the bioreactor.  The population I have pictured here is mature. because I know they have already eaten a lot of food and are now not interested in new food.  Also they are exhibiting this clustering behavior which I am guessing is related to mating or egg laying.  In the cluster they go into a crevice and orient towards a central point with their butts sticking outwards. The other thing I notice is these unidentified insects have, horizontal across the rear of their thorax, a white line or perhaps window into their thorax (black solider flys have something similar where you can observe eggs inside their thorax). I have only noticed this white line on the mature ones, and most of the insects in thsi picture exhibit the white line, you can see it in the clustered picture.  I believe they have 6 legs and 2 antannae, and they also might have 2 small legs near their mouth (but maybe thats their mandible or other mouth part).  

Thanks for your help, I am new to insects, but their life cycles are fascinating.

ANSWER: Dear Andrew - Your mystery critters look to me more like mites than insects, but I have not been able to locate any really useful information on this subject. If they are mites, the next question would be are they actually feeding on the flies, or simply using them for transport to another location (phoresy). I can only suggest that you look at the following sites, and make some queries there:
1. - Intensive Black Soldier Fly Farming

2. - Black Soldier Fly Blog

3. - Black Soldier Fly Forum

Sorry not to be of more immediate assistance,

---------- FOLLOW-UP ----------

QUESTION: Hi Ed, thank you for the response.  I am familiar with those links and I have reached out there.  I came to you because I wanted to get an ID on it.  I did not know that mites were not insects.  If that is true that it is a mite and not an insect than I would hope that would help me treat it.  For example I could focus on treatments that Arachnids do not like.  

Is there a chance that it is not a mite?  Are there any diagnostics that I could look for more closely to help in the ID?

Your idea about phoresy makes sense to me.  In that case the mite would not want to damage the fly.  For example, I believe I am seeing lower rates of flys coming out of the pupation box since I've seen the mites attaching.  That may indicate that the mites are doing damage to the fly... because why would they kill the fly if they were hitching a ride.

Dear Andrew - I really need to see a clearer enlarged image of the critters in question in order to be positive of an i.d. All that I can say at this point is that their overall appearance and your description of their behavior points in the direction of their being mites. If you examine them under a microscope, you  may be able to determine whether their first pair of long appendages are legs or antennae (some mites use their elongated first pair of legs in a manner that makes them superficially resemble antennae). If you see only three pair of true legs, they would not be mites. That aside, I am very hesitant to recommend any chemical (acaricide) control, as I have been unable to find any information on the effect(s) they may have on soldier flies. This is an area where I would expect that you should be able to get a good opinion at least from someone on the soldier fly blog or forum. Again, if you can provide a clearer and larger image of your unwelcome guests, I will be happy to attempt a more positive identification.

Entomology (Study of Bugs)

All Answers

Answers by Expert:

Ask Experts


Ed Saugstad


Will accept most questions in general entomology, including those related to medical entomology, taxonomy, ecology, arthropod surveillance, and pest management. If you are requesting a 'mystery bug' identification, PLEASE either attach an image to your question, or post an image on a web page (such as Flickr) so that I can look at it, as verbal descriptions frequently are insufficient for a definitive identification.


21 years in the U.S. Army as a medical entomologist; duties varied from surveillance of pest populations (including mosquitoes, cockroaches, ticks, and stored products pests) to conducting research on mosquito-virus ecological relationships and mosquito faunal studies. Ten years as a civilian analyst for the Department of Defense, primarily on distribution of vector-borne diseases worldwide. Limited experience on surveillance of agricultural insects in North Dakota and Indiana.

Entomological Society of America, West Virginia Entomological Society, Society for Vector Ecology, National Speleological Society, West Virginia Association for Cave Studies.

American Journal of Public Health, Contributions of the American Entomological Institute, Japanese Journal of Sanitary Zoology, Journal of Economic Entomology, Mosquito News, and Mosquito Systematics.

B.S. in entomology from North Dakota State University in 1963, M.S. in entomology from Purdue University in 1967.

©2016 All rights reserved.