Every now and then, you notice something catching a free ride — mites on a beetle, algae on a snail, or some tiny insect clinging to a bigger one. Sometimes I only spot them when looking back at photos.
Thought it could be fun to have a place to share those little tag-alongs if you’ve found any.
Every time I notice a arthropod on my car when driving, a variation of the thought “Would those genes ever have had a chance to spread here without me giving it a lift? Hope you like the change of scenery little guy.” pops into mind 
Maybe similar to Observations “hiding” in other observations; Share your examples!?
There are a couple of projects for animals intentionally hitchhiking on other animals, sometimes just for the ride, sometimes with more sinister plans:
https://www.inaturalist.org/projects/phoresy
https://www.inaturalist.org/projects/passengers-parasites-taking-rides
Yeah, sort of! :D
https://www.inaturalist.org/observations/213855033
Was literally in a kleenex box; no idea where it got in it
Arthropods are pretty good at self-distributing even without human help – we just extend the speed and distance of travel. Many of them have wings. Others hitch rides on creatures that do, or they travel on plant matter that is distributed by water or wind. Young spiders may use bits of web to travel aerially (“ballooning”).
What impresses me the most are the zooplankton who somehow manage to colonize seasonal puddles, often astonishingly quickly, in spite of the lack of any obvious route that would allow them to get there.
That is an interesting achievement, I have to admit. Travelling on birds? Came to mind as we have sporadic cases of swimmer’s itch, especially during bird migration, pop up in an artificial lake nearby. The city environmental administration says the flatworm eggs get to the lake attached to birds.
This photo immediately popped into my head when I saw this topic. It is from summer 2013 in Colorado. You can see a few orange mites hitching a ride on the legs of some young Eastern Box Elder Bugs. I posted the photo rather than the link for iNat as I wanted to do a better job editing the photo. It still isn’t great but is somewhat better than it was.
Since it is called a Smooth Turtle Leech I don’t know how truly “unexpected” it was, except to me since, it was a first for me. The leech has hitched a ride on a Striped Mud Turtle. Gainesville, FL.
I have frequently documented mites “riding” on carrion beetles and large ground beetles.
I learned that those mites are usually not parasitic in the strict sense but abuse the beetle for a free ride from one carcass to the next.
It is unclear to me if/what a possible advantage for the beetle could be.
Bees also often carry mites.
But there, I believe, they are real parasites and look for an opportunity to hijack the bee’s nest to feed their own offspring.
https://www.inaturalist.org/observations/264510947
Yes, birds usually get the credit. Some Cladocera produce resting eggs which can pass unharmed through the gut of a duck. And sometimes I guess the eggs just blow about when something disturbs a dry pond bed, but that would be a more random distribution so I think large aquatic creatures are more important vectors.
It was… I think a decade or so ago, that we started seeing mistletoe (Viscum album) in the wild here (Finland). It was quickly determined, that there was pretty much nothing that could be done at that point to stop the spread. The spreading vectors were traced through genetics to a certain collection of neighbourhoods in a small city next to where I live and determined the spread had started most likely around Christmas.
The hypothesis is, that there had been probably a real mistletoe door decoration (still an unusual choice), that had had berries. They are apprently sticky, so they probably go stuck to the feathers of birds, who then flew across a fjard to a forested island, from which two spreading vectors start and so on. Nowadays it’s pretty much everywhere. It’s really easy to see this time of the year, when the trees are without leaves. It started to become visible all around a few years ago. I’ve counted dozens of them within a 2 km circle around where I live, just on the trees along the main roads.
With the climate warming up, and even wine farming starting here… Well, Southern Finland just isn’t cold enough to kill it anymore.
I was so intrigued when I found them on the beetle:
Woah! That’s just crazy
Have you got mistle thrushes Turdus viscivorus? They feed on mistletoe - that is where the name comes from. And they transfer the seeds to other trees when wiping the stickiness off their beaks.
You can blame Loki for that one, the jerk.
