As you know this project comprises many different kinds of parasites, but most of them are from the animal kingdom with the greatest representation amongst the winged and once winged insects. Once cold weather comes to the Northern Hemisphere, it is much less common to observe insects of any kind active and many plants go dormant so it is a great time to

1. Savor the special finds one has made this year. (Thank you iNat for the Personal Year in Review. How rewarding and informative!)
2. Turn one's attention to insect observations in the Southern Hemisphere. Seeing what's happening Down Under keeps spirits up.
3. Learn about parasitic plants that are often more visible in the landscape in the winter time.

Check out https://www.inaturalist.org/projects/parasitic-plants-of-the-world a traditional project with anything but traditional plants. Or if you are interested in Eastern North America https://www.inaturalist.org/projects/parasitic-plants-and-hosts-in-eastern-north-america.
Wherever in the world you are, whatever season it may be, there is always something waiting to be discovered.

I have just asked for a new species to be added to the iNat universe. Meteorus stellatus is a braconid wasp with a gregarious cocoon cluster that resembles a star suspended on a thread. Please read the link for more details about this fascinating find.
https://www.eurekalert.org/news-releases/936083

Fantastic work, everyone! "The world is so full of a number of things..." How true that is when it comes to parasites and hosts. Who knew there were so many. Wow! With over 16,000 observations now we have a significant of amount of data to wonder at. Yet data is most useful when it is organized so that information can be located quickly again.
As we can on observations featuring hosts we will be filling in the observation field "Being parasitized by" with Mites, Microgastrinae, Campopleginae, and so forth. A note of thanks to all those who have already been faithfully annotating life stages and filling in observation fields. Your work matters!

This project has accumulated a lot of observations of visibly parasitized caterpillars. Some caterpillar species have hundreds of qualifying observations.

So now that we have this mass of observations, what can we do with them? One simple thing is to get a feel of rates of parasitism among different caterpillar species. Just compare the number of parasitized caterpillars in this project to the total number of caterpillars, species by species.

Here's that math for most-reported caterpillars in the project:

Carolina Sphinx (Manduca sexta)
386 parasitized of 6017 total = 6.4% of caterpillars visibly parasitized

Cecropia Moth (Hyalophora cecropia)
115 of 1690 = 6.8%

Regal Moth (Citheronia regalis)
124 of 767 = 16.2% (yikes!)

Saddleback Caterpillar Moth (Acharia stimulea)
70 of 1952 = 3.6%

Spiny Oak-slug Moth (Euclea delphinii)
51 of 661 = 7.7%

Of course, there are some potential issues with this methodology. Below is a quick list of some conceivable criticisms. Are any of these likely to change the rates significantly? Are there others that I'm overlooking?

• For my counts of parasitized and total reported caterpillars, I am looking only at observations where the intended subject was the caterpillar. So I could be overlooking observations of parasitized caterpillars that were submitted as observations of the parasite. Also, for simplicity, I am counting each observation as a single caterpillar, regardless of how many caterpillars are photographed.
• Are parasitized caterpillars significantly under- or over-reported on iNat? Maybe parasitized caterpillars are more likely to be photographed, either due to impaired concealment, or because they might arouse more interest in the observer? Or is the opposite true; parasitized individuals might become less active, and therefore less noticeable?
• One source suggested that a particular tachinid fly parasitizes only final-instar caterpillars. So photos of early instars don't necessarily represent individuals that will never be parasitized; they haven't yet reached the stage where they could be parasitized. If this is true then the percentages above are underestimates. (And in general, this is probably true even if parasitism isn't restricted to the final instar.) But maybe the percentages above are still meaningful in a relative sense, and you could still accurately make a statement like, "E. delphinii caterpillars are twice as likely to be parasitized as A. stimulea caterpillars."

And of course I am explicitly not addressing parasitism that happens in other life stages, like while pupating.

A big thanks to @claire146963 and many others for annotating the life stages in these thousands of observations.

Doug

We've passed 10,000 observations representing more than one thousand species. Wow! Not bad for a project started January of this year. It all began with the Cotesia congregata cocoons found while annotating caterpillars for Caterpillars of Eastern North America https://www.inaturalist.org/projects/caterpillars-of-eastern-north-america. Caterpillars inspired Passengers. Thanks @eraskin!

We'd be nothing without our active, worldwide membership. You grew this project well beyond Lepidoptera caterpillars and their parasites to encompass many other hosts and parasites in all stages of life. Your curiosity is a gift. Because of you, these often neglected organisms have the attention they deserve. Great job, everyone! Also special thanks to the manager and the curators for discovering and deciphering observations suitable for Passengers. You combine enthusiasm with expertise. Interpreting nature for others is second nature to you. Thank you!

Some goals for the future
*Put more countries on our map. Parasites know no borders, but some places are under represented at best.
*Include more observations of parasitoid eggs, larvae, and pupae. Life-stage annotations do matter!
*Connect more hosts with their respective parasites.

As Passengers: Parasites Taking Rides continues to grow we need even more members and curators. Find a region to watch, a taxon to explore, or to help to organize the sheer volume of data. We have come a long way. I'm eager to see what the next 10,000 observations will be. Take care!

Butterflies and moths do not lead carefree lives. The life of a Lepidopteran is a life of risk. From egg to larva, from larva to pupa, from pupa to adult--no stage is without danger. Each phase of metamorphosis has its own set of unique enemy organisms. I will name just a few of the parasitoids to expect at each stage. This is by no means an exhaustive list. Nor does this brief entry do justice to the intricate dance of life stages between each parasitoid and its chosen host.

Lepidoptera Egg
• Scelionidae wasps
• Chalcidoidea the wasp lays its own egg inside the host egg and its larva eats the host larva. The host eggshell serves as a pupal case for this parasitoid wasp which eventually emerges from the egg as a full-grown adult.
https://www.inaturalist.org/observations/42465072

Lepidoptera Larva
• Tachinid flies either lay eggs in or on the caterpillar.
https://www.inaturalist.org/observations/57509878
• Microgastrinae wasps like Cotesia lay eggs inside the caterpillar. Eventually, the wasp larvae emerge and spin papery cocoons either on or near the unfortunate caterpillar.
https://www.inaturalist.org/observations/4139426

Lepidoptera Pupa
• Tachinid flies,
• Chalcidoidea wasps such as Ptermalidae wasps insert eggs into the host pupa. The Ptermalidae young burst out of the pupa as fully grown adults.
https://www.inaturalist.org/observations/45315270

Lepidoptera Adult
• Insect destroyer fungus
• Parasitic mites most likely Trombidium
https://www.inaturalist.org/observations/56933237

Know the life stage to better understand the life risk.

I changed the name of the project from "Bus Passengers: Caterpillar Parasitoids & More" to “Passengers: Parasites Taking Rides“ to reflect how this project has morphed to include more than just lepidopteran parasites in the larval stage. Thank you in advance for your contributions.

While the Easter Rabbit is imaginary, tachinid flies are real. They hide their white eggs on caterpillars. See how many eggs you can find!

https://www.inaturalist.org/observations/34444826
https://www.inaturalist.org/observations/39041805

Some make interesting patterns.
https://www.inaturalist.org/observations/30991363

Some are hidden extremely well.
https://www.inaturalist.org/observations/17730216
https://www.inaturalist.org/observations/41351322

some hide near microgastrinae cocoons.
https://www.inaturalist.org/observations/12633680

Some tachinid eggs are really tiny!
https://www.inaturalist.org/observations/35588817

Wishing you a Happy Easter! Remembering the Resurrection gives me hope. Take care! Noelle Congdon

Here is a helpful resource that has been the work of our own project member Jose Fernandez-Triana and his colleagues. In his own words:

I am taking this opportunity to let you know that yesterday it was published a large checklist on the world species of Microgastrinae. It is open access and can be freely downloaded here:
https://zookeys.pensoft.net/article/39128/

Although is a technical document, it contains picture of all genera of Microgastrinae (although from dead specimens in collections) but it also have some initial sections where the group is explained and details on host biology are also briefly discussed. I thought that might be of interest to you and your team, and because the paper is free to access, feel free to pass the info to whoever might be interested.

Cheers,
Jose

I plan to refer to this myself to learn even more about these mysterious braconids. I appreciate the diligent research and years of study this list represents. Thanks so much! Noelle Congdon

Many caterpillars munch on plants which are highly toxic. For instance, the Tobacco Hornworm Manduca sexta can be found lunching on practically anything in the Nightshade family Solanaceae. Which includes: tobacco, petunia, tomato, pepper, potato, nightshade, etc. M. sexta can sequester these poisons and be unaffected itself. However, these plant poisons in the caterpillar's body don't stop the Microgastrinae wasp Cotesia congregata from turning the hapless caterpillar into an incubation chamber. Why? Are Microgastrinae unaffected by alkaloids, period? Or are they affected by some and not others? There are many different species of sphinx most of which are named after their different plant hosts. Does knowing the caterpillar's preferred food plant tell us anything about which wasps or even which tachinids will use it as a host?

Is the Catalpa Sphinx Ceratomia catalpae is really parasitized by the Cotesia congregata wasp? Or do plant alkaloids matter? The fact that the wasp cocoons are larger and fewer in number than those seen on M. sexta makes me wonder if it is indeed a different species of wasp. There is vast difference in width between these two varieties of Sphinx caterpillars. Is this difference in mass a superficial difference only? Or does it affect the choice of parasite? For that matter C. catalpae. is much skinnier than most of the other Sphinx caterpillars which makes me wonder if it shares less genetic material in common with the other members of the Sphinx family.

Take the challenge and raise the wasp cocoons from C. catalpae or some other variety of sphinx caterpillar to see if they do indeed turn out to be Cotesia congregata or some entirely different species or genus of parasitic wasp.