Releasing butterflies and moths

Strong opinion alert.

Releasing butterflies and moths into the wild: it can make for such innocent scenery. But is it really okay to do so? I think that not many people are aware that they could be actively contributing to the destruction of our native wildlife and our hobby too. I know that sounds very harsh, but let me explain! Sadly, I get more e-mails and messages about releasing livestock in the wild than I was hoping to recieve, and to me it seems to be a worrysome trend.

Native versus non native species

Thus I would really like to emphasise one thing on my website: do not ever try to release non-native, exotic species. Please be a responsible owner. I know that the idea of having a large, colourful exotic species in your neighbourhood can be very exciting. But the ecological implications can be enormous, and a potential disaster for native wildlife. Don’t do it.  And if you are thinking about it, please read this page so I can change your mind. This is one of the very few things I am very strict about. I honestly believe that people doing these sort of introduction projects by themselves should be banned from keeping animals for life. Please don’t be ignorant!

PART I: Releasing non native species:

I’ve heard it countless times. “But, it’s just a butterfly! How can they have a negative impact?”. Maybe it doesn’t even feed on plants that are found in your country and is probably unable to reproduce. Maybe they will probably not survive the winter. Or maybe you think they have a negligible impact on your local flora and fauna. Let me tell you why you’re wrong, and even the most seemingly harmless butterflies and moths can make a disasterous impact when released in your local environment.

A) Diseases and pathogens

Populations of butterflies and moths are often suppressed by a wide range of viruses, bacteria and parasites. Any foreign species of butterfly or moth is potentially a carrier of these disease vectors. If these pathogens are allowed to spread to continents they are not native to, they can potentially wipe out native species. In many cases, due to coping with these pathogens for millions of years, the animals affected by them evolve some degree of resistance or immunity to them. However, species that have not been in contact with these pathogens may not have any resistance to them.

For example: all European amphibians being threatend by a fungus, Batrachochytrium, that comes from released Asian salamanders, and is now nearly driving some species to extinction. Asian salamanders are resistant to it, European ones are not. And it spread from exotic pets to amphibians in the wild. Now it’s destroying our species. Thank you very much hobbyists! Here’s another example.  My country, the Netherlands, has  only one species of native crayfish: the European crayfish, Astacus astacus. But it’s existence is being threatened. Responsible is the “crayfish plague”, a type of water mold that attacks crayfish. Where did that come from? It came from exotic crayfish that have been introduced here. In the Netherlands, 14 species of crayfish can currently be found, while the European crayfish is the only native species. That means we have 13 invasive species of crayfish! Interestingly, these exotic crayfish species carry fungal spores that infect them. However, none of them are as susceptible to them as our European crayfish – simply because of the fact that  the European crayfish, Astacus astacus, has never been in contact with this disease, and has never developed resistance to it.

In some instances this effect is even observed in humans. Maybe some people will remember the fact that Native Americans, due to the lack of prior contact with Europeans, had not previously been exposed to the diseases that were prevalent on the distant continent. Therefore, they had not built up internal immunities to the diseases or formed any medicines to combat them. When European settlers and colonists explored the American continent, millions of Native Americans were wiped out due because of the flu, smallpox, tuberculosis and more diseases that proved to be much more dangerous to Native Americans than it was to the Europeans that were resistant to it in some degree – or atleast, more resistant.

Do you think such a thing won’t happen to butterflies and moths? Think again! Some species even carry their own diseases or pathogens. Take the monarch butterfly, Danaus plexippus, a famous one – it carries a protozoan parasite, Ophryocystis elektroscirrha, that as far as we know only infects monarchs. Or did you know that a bacterial parasite called Wolbachia once nearly wiped out the Hypolimnas bolina population on the Fiji islands?  This parasite kills males only and has causes some nearly all-female broods to emerge, reducing the male population of this butterfly to less than 1%.

Even if they are not carrying foreign diseases or pathogens, non native species can be vectors for native kinds of pathogens. For example, a newly introduced moth species could be a great host for a native species of parasitic fly or disease, disproportionately increasing their numbers, which may affect native species that are targeted by this pathogen too. You simply don’t know. This is why releasing anything exotic in your environment can be a foolish  act.

B) Unforeseen interactions

Some species of butterflies and moths sequester toxins and are poisonous. Birds and mammals that co-evolved with them know this, and avoid them, or have become resistent to their toxins. Take the monarch butterfly for example: in America, birds know to avoid it and its bright orange warning colour. However, in other continents, birds may not be familiar with the butterfly and may become sick when they consume it or feed it to their young.

This is one example out of many potentially unforeseen species interactions that can happen. From hybridisation with native species, from interfering with host plants and predators, from spreading disease and fungi, from competing with native species and potentially outcompeting them, non natives can affect native ecosystems in several negative ways. Maybe a newly introduced moth species is a good food source for an insectivorous bird that normally feeds on other kinds of native moths. Imagine if it suddenly prefers eating the invasive species, which in turn, increases the population of the other  native species, since they are not intensively being hunted anymore. This may warp the entire environment, for an increase of moths means an increase of feeding damage and pressure on the plant species they feed on, and so forth. I think it would be very ignorant to claim that your introduced species will not have much impact, for nobody really has the knowledge to predict that fact. Ecosystems can be very complicated. You simply can’t know. In some cases butterflies and moths can even adopt new host plants in new habitats. They compete for food with native species that are possibly already suffering. They change the dynamics between predator and prey.

C) Invasive species

When established, non native species can outcompete and wipe out native species. Lepomis gibbosus, the sunfish, outperforms native fish in the Netherlands and consumes them until only they are left. Prunus serotina from America destroys entire forests in Europe, where it forms homogenous patches of only Prunus serotina instead of woodland. The gypsy moth, Lymantria dispar, is unstoppable and consumes entire forests in America. The list goes on and on.  From pythons in the Everglades to the rats on the Galapagos islands that eat the eggs of all the native giant tortoises, that are  almost completely unable to reproduce now and will probably go extinct due to the rat invasion, invasive species are threatening biodiversity all over the globe. Please don’t be as arrogant to think you know best, and decide that your favorite species of butterfly or moth will not have a negative impact! Many of the introduced species were introduced that way: by hobbyists that released them because they were cool or pretty!

All in all, even if the species you want to release has no chance of establishing itself, releasing a few individuals can already be harmful and may yield unforeseen consequences that will negatively impact your local flora and fauna. In my opinion it would be total ignorance to argue against this, seeing the tons of examples around the globe where it has gone wrong, and still wanting to release non native species with this knowledge in mind, would be a malignant act.

D) The hobby argument

Even if you are somehow not convinced of A, B, C and D then consider the following simple fact. Governments work around the clock to take measures that prevent invasive species from spreading. Should you release a non native species in great quantities in your local environment, consider the fact your goverment will be quick to ban this species from the hobby if mistaken for an invasive kind of insect. There are a few examples of animals being banned by the government because of irresponsible owners. In most cases, these have not been butterflies or moths but rather birds, snakes, lizards or frogs that were released by their owners and were found to survive for extended periods of time, even while not reproducing in most cases. However, imagine how sad it would be if your goverment ended up banning your favorite species because somebody else has decided to release them. You would be ruining your hobby for yourself and others.

PART II: Releasing native species:

I think that in principle, the rearing and releasing of native butterflies by hobbyists is a bit of a grey area. Depending on the species it can either have no impact at all or a negative impact. It will certainly not make a positive impact. 

In the case of locally found, common and widespread species  I would say it is pretty harmless. Although if done with the wrong species it may cause an accidental introduction of species not native to that exact area, which may or may not have a negative impact – introductions are not considered a good thing.  On the other side it would be pretty extreme to deprive people of the importance of studying the life cycle of a butterfly, something that cultivates interest in these creatures, which is getting rare nowadays.

So in my opinion, any releasing of insects in the wild must be done responsibly. Also it depends on your motivation for doing it: hobbyists should not consider doing this to re-introduce or “help” butterfly species in large numbers. Breeding and releasing them can have a negative impact if done in very large numbers, and will rarely or actually never make a positive impact, unless done so in co-operation with habitat improvement guidelines.  

You releasing butterflies or moths does probably not make a positive impact 

There seem to be a good amount of people that think that producing more individuals of a species helps them. This can only be true in very rare cases, such as nearly exctinct species of mammals and birds. But in no way can we compare rare butterflies and moths to pandas or rhinos. In fact, breeding and releasing large amounts of individuals has a bigger chance of harming them than helping then.

The populations of butterflies and moths, in the wild, are heavily regulated. They are, as insects that are on the bottom of the food chain, extremely disposable as individuals – millions of them die every day. Even the rarest species of them consistently end up as food for birds, rodents or wasps, are targeted by bacteria, protozoans, parasites, fungi and more. This is why they in many cases lay great numbers of eggs:  in some species of butterflies and moths, the recorded survival rates in the wild have been less than 1% per individual. Although this differs per species and is an extreme example, it illustrates why breeding and releasing many individuals is not the right approach.

You see, the amount of individuals of a single species that are alive at any given point in time, and the range they cover, is decided by their habitat. The amount of individuals that survive, are exactly the amount of individuals that are supported by the environment. Releasing more individuals does not change the amount of individuals the environment can support. Even if we look at the rarest species in the world, their populations still consist, in many cases of over hundreds or thousands, but in most cases millions of individuals. However, these individuals are often very restricted to specific types of habitats. As you know, most butterflies and moths are specialists that only feed on certain types of plants within certain habitats. This means they aren’t free to survive and reproduce wherever they want to. They are dependent on the plants they feed on and the environment that caters to their specific needs, as they have been adapted to survive in this specific environment.

The same habitat that provides for all of their needs, presents them with numerous challenges. From predation to a limited number of food plants (competition!) to variations in local climate to outbreaks of diseases and parasites, the suitability of their enviroment fluctuates a lot, and drives numbers up or down.

In a stable, established population, the amount of individuals within a certain habitat are exactly the amount of individuals that the environment can support. You see, if the number of individuals goes up, then problems will arise: due to the high number of individuals of the same species, competition will increase, and so will the infection rate of parasites, diseases and viruses. Many pathogens thrive in an environment where there is a high density of individuals that can infect eachother: food will become scarce as the high number of individuals will have to compete for it, and the numbers will go down as a result. If the number of individuals goes down, the opposite happens: food becomes more freely available, pathogens are less chance to spread, and there will be no competition: the number will go up. Populations fluctuate naturally: they inflate and then collapse, but will to some degree always stabilise around the number of individuals the environment can support. 

It is evident that populations of butterflies and moths are pretty self-regulating. To sum it up, the amount of individuals that survive, are the amount of individuals that can be supported by the local environment. 

Boosting their numbers does not help them, for if the number of individuals of a species are increased, so will the pressure they exert on the environment. In return, their numbers or reproduction and survival rates will decrease. Even if you would release millions upon millions of them, the amount of individuals that survive would probably revert back to the original amount in a very short time. Instead, their habitat should be improved. This can be done, for example, with managing the habitat to provide adequate food plants, nectar plants and more. Habitat destruction is the biggest threat to Lepidoptera for they are entirely dependent on their specific habitats. An increase in the surface area of suitable habitat means a greater amount of individuals can be supported by the environment and will increase their numbers in a sustainable way. Mass breeding and releasing can only do harm, as this will artificially increase the pressure on the natural populations, forcing them to compete with individuals that may not be supported by the environment. That being said, breeding projects can save species from extinction, as long as they are combined with efforts to manage the habitats correctly.

If you want to release butterflies and moths choose locally caught, native species. 

Releasing a native species can have a negative impact too especially if the livestock is from a different geographical location. Even if they are the same species, it does not mean they are the same kind of animal. Some species feed on different plants in different countries and have different overwintering strategies and/or habits. They can be different subspecies, or even if they aren’t, they may be adapted to different environments.. this means they will be less suited to survive in your country, and may potentially hybridise with the moths in your local environment to form ‘weaker’ offspring that may struggle to survive in your local environment more.

If you want to help butterflies and moths, plant host plants and nectar plants and work on improving their habitats. Reckless introduction or rearing and releasing projects are to be discouraged, although often done so by people with good intentions. Make sure to spread awareness and education, which is also vital for our willingness to preserve them. 

Thank you for reading my article. This is the end of this page. Below you will find some useful links to help you navigate my website better or help you find more information that you need about moths and butterflies. 

Dear reader – thank you very much for visiting! Your readership is much appreciated.  Are you perhaps…. (see below)

Citations: Coppens, B. (2019); Written by Bart Coppens; based on a real life breeding experience [for citations in literature and publications] 

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