“Black Death” is a general term used by non-scientists as if it is a disease. It is not a disease. It is a sign of disease or other problem. It is often a way of saying, “my caterpillars died and turned dark and I don’t know why they died.” Let’s look at some of the reasons why caterpillars may turn dark or black just before or when they die.

Each of these photos are of dark colored caterpillars or chrysalises. Please stop reading a moment and look at each of the first four photos. If you are raising caterpillars indoors, it is important to know WHY they turned dark and died or died and turned dark.

The way you would clean up after some of these differs greatly. The way you would clean up after the first photo’s problem, the second photo’s problem, and the third photo’s problem can vary greatly. If you switch the way you clean up after the problem, you may end up continuing the problem.

Looking at the first four photos, many people would say they all died from ‘Black Death’. In each photo, the caterpillars or chrysalises turned dark.

Image #1 – the chrysalises are infected with chalcid wasps, a parasitoid. You can learn more about chalcid wasps by clicking on this sentence.

Treatment: If this happens in your home or rearing operation, you should move all your caterpillars to another room and place all your chrysalises in a sealed container or a container with so fine a mesh that they cannot escape from the mesh container. When the wasps emerge from the chrysalis, they immediately mate and begin laying egg in other soft chrysalises.

Image #2 – this Monarch caterpillar died from bacteria entering its hemolymph (insect ‘blood’). Many things can cause bacterial infections in a caterpillar or chrysalis.

Treatment: If this happens in your home, you should disinfect your rearing containers as well as your tools and raise fewer caterpillars in one container until the problem ends.

Image #3 – this Gulf Fritillary caterpillar died from NPV – Nuclear Polyhedrosis Virus. This is a frightfully contagious virus that passes from one caterpillar to another extremely fast.

Note: If you bring in a caterpillar and it has NPV, the chance of raising it to become an adult are nearly zero. In the wild, NPV is more prevalent in the fall. You can learn more about NPV by clicking on this sentence.

Treatment: If this happens in your home or rearing operation, you should euthanize all caterpillars in the same rearing container. Rearing containers and tools, table tops and light switches, toilet handles and door handles, refrigerator handles and EVERYTHING should be disinfected with bleach water solution or bleach wipes. Virus particles are small and are easily transferred from a rearing container to everything else. It is important to wash your hands well BEFORE and AFTER touching caterpillars. When you bring in new caterpillars, disinfect their food before feeding it to the caterpillars. Food can be disinfected by soaking them in a 95% water and 5% bleach solution for three minutes followed by a thorough rinse and a pat dry. Outdoors, nature can spread NPV as fast as the wind.

Image #4 – this Gulf Fritillary chrysalis is infected with chalcid wasps.

Treatment: Same as #1.

As you look at the rest of these photos, it becomes clear that death from one disease can cause appearance very like another. A butterfly cannot die from ‘Black Death’ because ‘Black Death’ is a comment on the appearance of the caterpillar or chrysalis when it died.

A caterpillar’s appearance from a death from some predators and/or parasitoids resemble the appearance of death from some diseases.

It is important to know WHY they turned black and died or died and turned black.