 The Question: Can you help solve a mystery with my wife’s first butterfly garden for monarch butterflies? She has had a chrysalis hanging on a watering can but it changed from jade to completely black and now we see it has a 3mm round hole in it. We opened it with a scissor and there in only a remnant left on the inside. We have not seen a successful exit yet. What could possibly have happened? Is this the result of a predator?Submitted by: John, Florida, USA |
The Short Answer: John didn’t attach a picture, but the 3mm (1/8) hole he describes is exactly what is left after a parasitoid fly larvae exits a monarch chrysalis (Danaus plexippus). A parasitoid insect lays its eggs in, on, or near a host, and the larvae then consume the host, often while it is still alive. Tachinid flies, primarily Lespesia archippivora, are major parasitic predators of monarchs, with one study showing that tachinid flies killed 13% of monarch caterpillars and chrysalises. Monarchs often contained three, and sometimes as many as ten, fly larvae. Some people who raise monarch butterflies advocate for killing the fly larvae by squashing any caterpillars or chrysalises that shows signs of parasitism, such as chrysalises that begin to turn dark. I suspect this isn’t particularly effective because it would make such a small dent in the tachinid fly population. I’m not sure there’s much that could be done other than keeping the caterpillars and chrysalises under netting. It might be that you have to just accept that 10-20% of monarch caterpillars won’t turn into butterflies.
For more information and pictures of a tachinid fly exiting a chrysalis, go to:
http://www.monarchlab.org/lab/research/topics/Enemies/Default.aspx.
More Information: There are about 8,000 species of flies in the family Tachinidae, all of which are parasitoids. Their primary prey are butterflies and moths, but there are tachinid species that prey on other types of insects and even some that prey on scorpions and spiders.
The idea of a fly larva eating a monarch caterpillar from the inside out seems pretty awful, and descriptions of this kind of parasitism always make people shudder, especially when the victim is a charismatic creature like the monarch butterfly. But as creepy as the lifestyles of parasites seem, anyone interested in the natural world has to accept that parasites are a major part of every ecosystem. In fact, biologists estimate that parasites make up at least half of all animal species on earth. But studies of animal abundance versus size show that parasites are always less common than other similarly sized creatures, suggesting that being a parasite is actually a tough way to make a living.
Sources:
Oberhauser, K, Gebhard, I, Cameron, C, et al. (2007). Parasitism of monarch butterflies (danaus plexippus) by lespesia archippivora (diptera : Tachinidae). The American midland naturalist, 157(2), 312-328.
Hechinger, R F, Lafferty, K D, Dobson, A P, et al. (2011). A common scaling rule for abundance, energetics, and production of parasitic and free-living species. Science, 333(6041), 445-448.
Most Tachinids are invaluable biological controls, attacking a number of insect larvae that destroy crops or garden plants. There is even one that feeds on Japanese beetles. The species that feeds on monarchs, Lespesia archippivora, also attacks a number of pests. It is even used as a biological control in some cases.
All and all, Tachinids help cut down on pesticides because they are such good pest controls. So, indirectly they help monarchs more than harm them. It is also good to remember that monarchs and Tachinids have coexisted for many thousands of years without going extinct. It is us and the things we do that pose the biggest threat to this and many other species.
http://nativeplantwildlifegarden.com/more-garden-friends-parasitic-flies/ Garden Friends: Parasitic Flies
Beatriz, I agree!
All Monarch caterpillars I bring in have the Tachinid Fly. My rate is 100% and I doubt 13% is a good estimate. I lost hundreds this year and used Ziploc bags to freeze the caterpillar. I used a box of 100 bags in September.
Can the Tachinid Fly smell them? If not, then how are they finding all of my caterpillars? I always have a lot of them since I have 29 Tropical milkweed plants.
I need to get rid of them from my yard!
We are currently getting a 100% death rate of our monarch butterflies due to the tachinid fly. There must be something that can be done to eliminate them from our yard. We are considering the elimination of the butterfly bushes so we don’t have to witness the carnage. the 13% mentioned in the article is ridiculous. Monarchs are in trouble, and tachinid flies are a major part of the problem.
You need to quit treating the tachinid fly as some sort of an organic godsend, and begin to look upon it as another major pest that needs to be controled .
Hi Douglas, I’m sorry to hear about your monarchs. Have you tried asking http://texasbutterflyranch.com/ for help? They are much more knowledgeable about rearing monarchs than I am. I can appreciate your frustration. I’m not involved in raising monarchs, so I can take a wider view, which is that the world is full of parasites and they are a natural part of ecosystems. The fact that I have a naturalist’s respect for the adaptations and their role as predators, doesn’t mean I like what they do to a species in trouble like monarchs. Having just had my puppy undergo minor surgery a few weeks ago to remove a botfly larvae, I’m not all that fond of insect parasites right now. The trick is how to control a parasite like the tachinid flies without doing further harm. See if Texas Butterfly Ranch has any suggestions. As for the 13%, the fact that you have 100% loss in your yard doesn’t mean the 13% figure is wrong, it just suggests that other yards have lower predation. Good luck!
I have lost all but one so far and it is truly disheartening – I feel I should just give up. That’s why when I hear 13% I figure I am doing something totally wrong. However, I follow all the precautions. I must make up 6% of the total 13% – I read on one site that the success rate in the wild is 5% between all the things that can go wrong. Based on my average – they are better left alone in the wild.