This Was From A 2015 Study By Fossette Et Al. Which Observed Wild Rhizostoma Octopus Jellyfish, Aka Barrel

Invertebrates are definitely capable of learning! A lot of people who don’t know anything about bugs say they’re automata who just do everything by instinct like an if-then computer program, and they absolutely have not looked into it because there’s SO much literature on invertebrate cognition including learning. One of the neatest papers I’ve seen was about Drosophila fruit flies (there’s a ton of fruit fly literature cuz they’re a common lab animal). So when a female fruit fly is exposed to parasitoid wasps, she will start laying fewer eggs. These researchers showed that fruit flies who have been exposed to wasps can communicate the presence of a threat via wing movements to other female fruit flies, and those flies will start laying fewer eggs too even if they haven’t seen the wasps at all, an example of social learning.

But what’s more: they can communicate threats like this not just with flies of their own species, but with flies of closely related species too. If the species are too distant, they stop being able to communicate as successfully HOWEVER these authors showed that if you house a bunch of flies together in mixed-species groups, afterwards their success at communicating goes up! This suggests the existence of a fruit fly “language” which differs between species, but which they’re capable of learning other species’ languages as well! Sources: 1, 2

see also this very scientific diagram from here:

One interesting thing about those studies is that they found that if you raise a fruit fly in isolation from hatching, it won’t be able to communicate as well. This suggests that there’s a critical period of socialization which flies require to learn how to do communicate properly and without it their ability to do so is impaired. (I believe there’s other studies on how other social interactions are affected by social isolation but I haven’t read them; again there’s sooo much fly literature ^^)

Another cool one I’ve seen is on antlion larvae, who hunt by digging pits and then waiting in the middle for ants and other bugs walking by to fall in. It’s generally thought that sedentary animals have fewer cognitive capabilities than mobile ones, due to their less demanding lifestyle, however these studies (which I’ve only skimmed) have been carried out which demonstrate that they are still capable of learning. Specifically, they can be taught to anticipate and identify approaching insects based on vibrations in the sand, and will subsequently adapt their behavior to hunt more efficiently! Even animals with what seems like a simple feeding behavior are still very capable of modifying it, which makes sense evolutionarily; while obviously different animals will require different levels of intelligence, you can imagine in a lot of cases that being able to modify your behavior based on experience is distinctly advantageous. Source 1, 2

Not an arthropod, but another bug that there’s been a lot of research into is Lymnaea pond snails, which are another common model organism for studying neurology and cognition. A ton of work has been done on their capabilities for associative learning, i.e. classical conditioning (“dog learns to salivate at the ring of a bell”) and operant conditioning (“rat learns that pressing a button gives food”). It’s been found that their ability to learn is actually a lot more complicated than just those simple kinds of stimulus ↔ response. They can take stuff they’ve learned in stressful situations (simulated experimentally by exposing them to the smell of crayfish, which eat snails) and generalize it to situations beyond just the original context, which you can imagine must be pretty important for surviving in the wild. Conversely, they can also place memories in context: when taught stuff in the presence of both crayfish smell and carrot smell, subsequently they will recall what they’ve learned in response to the carrot smell alone; in other words, they’re not just learning “carrot + crayfish smell”, but “carrot smell = crayfish smell”, placing their memories in the broader context of their environment (which again, must be helpful for survival). So they can not just learn but pretty flexibly as well! Sources 1, 2, 3

This isn't a bug at all but pretty recently there was a study that found that box jellyfish are capable of associative learning. This one research lab has done a lot of work into vision in the Caribbean box jellyfish (they have eyes btw) on both a behavior and a neurological level and have found a lot of cool things, like that these box jellyfish use their vision to navigate through their habitat of mangrove forests, and that though they don't have a brain as such, they do have a central nervous system in the form of a ring nerve connecting four small clusters of neurons that process and combine input from their eyes. I can't actually read the paper (paywall :P) but last year they did an experiment where they put jellies in a tank with darkened bars on the glass to simulate mangrove roots. Normally the jellies gauge the distance to a root by how dark it appears and then swim around it when they get near; however the bars in the experiment were colored so that they looked like they were farther away than the wall actually was. At first the jellyfish kept bumping into the all, but after several rounds of trial and error they began to avoid them, indicating that they were able to learn from the experience! Jellyfish! Aaaaa nature is so cool. Source 1, 2, 3

I have a question! About bugs and arachnids and all them. Sorry to lump them all into one category, but I'd rather not make the same post multiple times.

My question is: Can they learn "tricks?"

By this I mean are they capable of learning, in general, I suppose. Like mice in a maze, magpies with a rock.

Also, what sorts of things have they learned? How do they learn (like watching others or from experience)?

I ask because it's something that really interests me. I know the ability to learn doesn't add or subtract value from a being, it's a curious thought as I know very, very little about beetles, and spiders, and bees, and so on!

Do they just know how to do things because it's all their kind have done since the beginning of them? Do they have to learn or are capable of it?

The first image linked is not actually a priapulid but a sea cucumber in its spawning posture! It was misidentified on iNaturalist and went viral before it was corrected— see the original observation here. (It gets kinda heated which I think is kinda funny. Penis worms are serious business!) I have always said before that I want internet fame specifically for two reasons: to make PSAs about Anomalocaris’s head carapace which everybody always leaves out of drawings because of that one inaccurate museum model, and about the incorrectly identified sea cucumber photo about which is now like the first image result you get when searching for penis worms and is my NEMESIS 😠 (the misinformation, not the photo or the sea cucumber, those are great)

For all the worm fans— priapulids are super easy to identify; there are as of the time of writing only 22 recognized species, and for many of them the only photos of them are from articles in scientific journals. Over half the species are microscopic, and the macroscopic ones are mainly found in polar regions, often in the deep sea, where they are usually burrowed in sediment and thus are little-encountered by people. The only one of them that is commonly photographed (and studied) is Priapulus caudatus, which is broadly found across the northern northern hemisphere even in shallow waters and I think probably has to be the most accessible species in general. They look like this:

image by Thomas Trott

This species accounts for probably 99% of the images of priapulids out there, and its relatives look rather similar, such as its southern hemisphere counterpart Priapulus tuberculatospinosus or the two-tailed species Priapulopsis bicaudatus. The intricate, feathery tails (referred to in the literature as “caudal appendages”) are probably the most distinctive feature of this group; they are believed to be involved in respiration, though as with many things about the phylum it is not known for certain. (See this recent paper for a review of macroscopic priapulid morphology.) In the zoomed-out photos of that sea cucumber you can see on the iNat page, it lacks a tail which is a dead giveaway that it is not any of these; also note that while it has some longitudinal striations along what sorta looks like a proboscis, they don’t actually bear any teeth! The spined, toothed proboscides of priapulids are indeed super cool and are their most distinctive feature setting them apart from other proboscis-bearing worms like peanut worms or spoon worms, which are often also misidentified online as priapulids. A fun fact is that the shape of their teeth varies across species in a way that appears to be closely correlated with their diet, see this paper for a neat study that uses tooth shapes to examine the different ecological niches occupied by extant priapulids and their Cambrian relatives!

The only other macroscopic priapulids that don’t look much like Priapulus are the two species Halicryptus spinulosus and Halicryptus higginsi, the latter of which I believe there are literally like two full-body photos in existence of it, one of which is from a login-walled journal article from 1999 and the other of which is one of the specimens from that 1999 article photographed after 25 years preserved in a museum. There’s a decent number of photos floating around of H. spinulosus (though still not as many as P. caudatus); they look like this:

image by Claude Nozères

As you can see, Halicryptus lack tails and have a much less prominent proboscis than Priapulus and its relatives, which you can only see the spines of on the very tip; H. spinulosus in particular has a rather short and small body that distinguishes it a lot, while H. higginsi is the largest known species of priapulid in the world (see this paper for a review of both of them). They’re maybe less distinctive-looking but idk, I don’t know off the top of my head if there’s super anything else you would mistake them for, and images of them are pretty uncommon anyway. In any case as far as macroscopic priapulids go, these are the only ones you have to look out for; if you’ve got those down you’re all set! As stated before, most priapulid species are actually microscopic; just for fun here’s the tropical meiobenthic species Tubiluchus corallicola:

image by Museum of Comparative Zoology, Harvard University

look at that squiggly tail!

And yeah in conclusion priapulids are super cool and underrated and I wish there were more people paying attention to them; there’s soooo many neglected taxa that we’re still only just discovering basic aspects of their biology and priapulids are one of them! If you want to see their amazing extensible proboscis in action, linked below is by far the best priapulid video out there, I highly recommend it. And most of all remember everybody THAT PHOTO IS A FRICKING SEA CUCUMBER, NOT EVERY WORM THAT LOOKS LIKE A PENIS IS A PENIS WORM AAAAAAA 😭😭😭

Can't believe any real animal has teeth as awesome as penis worms have.

They are meat eaters :)

I like making bets about things that happen in the far future and being like “if I’m wrong you can bring me back from the dead and say I told you so”, except haha sucker I’ll be long-eaten by flies by then, and those flies will have been eaten by toads and those toads will have been eaten by more flies; can’t bring me back when my atoms are already recycled and scattered all across the web of life, feeding and being fed upon, fluttering through countless existences before inevitably moving on; how many lives I have lived, how many lands my substance has visited, I am in the air and the water and the rock, how can you bring me back when I am already here

if you do bring manage to bring me back though you’ll have to also bring back a bunch of flies and toads and stuff so have fun with those

bugs are always cleaning their damn antennas

some standard and heirloom pumpkaboo varieties 🎃

this isn't related to cephalopods at all, but re: bilateral symmetry, there's actually some fairly recent (like, last 15 years) evidence that cnidarians actually evolved from bilaterally symmetric ancestors! Contrary to popular belief, a lot of sea anemones and coral polyps, though externally radial, actually have a bilateral digestive system. This could be a case of convergent evolution, but what's really remarkable is that embryonically, cnidarians develop this bilateral symmetry the same way as bilaterians, *using the same regulatory genetic pathways*! The polyp body plan is considered to be the ancestral state for cnidarians, while the "simplified" swimming jellyfish body plan probably is a secondary development, as suggested by the cnidarian fossil record and evidence of loss of body patterning genes in jellyfish. Together, this suggests the really exciting hypothesis that bilateral symmetry is actually the original ancestral state for the common ancestor of cnidarians and bilaterians, and rather than bilaterians being the ones who made the innovation of bilateral symmetry from radial, cnidarians would be the group that altered their symmetry instead! Sources: 1, 2, 3

(Echinoderms like starfish also are secondarily radial; they have bilateral larvae who undergo a very weird metamorphosis into their pentaradial adult form. Search "brachiolaria", "pluteus larva", or "auricularia larva" for pics!)

It's also a common misconception that cnidarians don't have central nervous systems. They're often said to have merely diffuse "nerve nets," and they do, but they also have a condensed ring-shaped nerve that integrates signals from across the body, basically constituting a central nervous system in all respects besides not actually having a singular "brain". In particular, there's been a lot of research into the nervous systems of box jellyfish, which are probably the most specialized among cnidarians due to their unique possession of true image-forming eyes, which they use for navigating both long and short distances as well detecting prey. One study from just last year even found evidence that box jellies display associative learning! Sources: 1, 2, 3, 4

(I believe there's also been research into the learning capabilities of echinoderms but I'm not as familiar with the literature. I know starfish do actually have image-forming eyes on their arms, which at least one species uses to navigate, though they also definitely do a lot of smelling and stuff as well. Source: 1)

Imagine yourself submerged in the prehistoric ocean. There are no fish, instead the only life forms consist of feather-like sessile organisms that sit on the seabed, filtering the current. The early organisms that evolved out of this, such as Jellyfish and Starfish, had radial anatomy. Their body structure entails a central axis from which you can split everything else. These bodies are simple, not designed for active mobility, lacking a ‘forwards’ or ‘backwards’. They didn’t even have eyes, instead interacting with and responding to the world via photoreceptive cells. What emerged from this were two developments: the evolution of complex eyes and the emergence of bilateral anatomy in early vertebrates and arthropods. In contrast to radial anatomy, bilateral anatomy entails an organism that can be split down the middle with rough symmetry. This is to say that they are built for direction. A body that is built for mobility entails significantly more complex behaviour behind its operation. Behaviour, in this sense, also becomes significantly more directed. These creatures now living in the ocean or on the sea-floor now begin to directly interact with one another. The mechanisms facilitating this interaction become pretty apparent in the fossil record; eyes, claws and antennae. The evolutionary consequences of this are the emergence of a complex nervous system alongside the presence of predation and, as Godfrey-Smith puts it “[From this point on] The mind evolved in response to other minds”. 

pretty princesses

Oftentimes I see people just make shit up about bugs and other invertebrates. People will say stuff like "actually it's been scientifically proven that insects are physically incapable of cognition" with no source, and then you look it up and in fact there is tons and tons of literature reporting results on this exact thing. A while back after getting into an argument with people online about wasps, I decided to try compiling sources on invertebrate cognition out of spite and I had to take a break at some point because there is so much literature out there, it is actually overwhelming. Just with fruit flies alone, there's studies on how they form stable social networks and fight to establish hierarchies; how they make group decisions and act differently in crowds; how they pay attention to what other flies are doing and teach and learn from each other, even with other species. When subjected to pain out of their control, they can develop depression and respond to SSRIs to the point that they are literally used as animal models to study how to treat depression in humans. And that's just like, one animal!

Even with all the research there is though the truth is that we just haven't studied things like cognition, perception, behavior, sociality, etc. for the vast majority of invertebrates (i.e. the vast majority of animals). Most behavioral research (honestly, just bio research in general) is focused on vertebrates -- particularly mammals -- and the research that has been performed for invertebrates has still only been done for a small handful of species and lineages. Fruit flies are one of the single most studied organisms in the world (and there's still a lot we don't know about them). If idk, clams felt emotions, do you think you would be able to tell by just looking at them? (I have no idea if they do or not, I don't think anyone has studied this. we do know scallops can see.) But absence of evidence is not evidence of absence, and given the small glimpses of insight we have gotten into the vast world of unknowns, I think yeah it's pretty obvious that there is way more going on with a lot of animals than people think. Scala naturae my behated

It's always so weird to come down from the biology heavens to see what the average person believes about animals, plants, ecosystems, just the world around them. I don't even mean things that one simply doesn't know because they've never been told or things that are confusing, I'm talking about people who genuinely do not see insects as animals. What are you saying. Every time I see a crawling or fluttering little guy I know that little guy has motivations and drive to fulfill those motivations. There are gears turning in their head! They are perceiving this world and they are drawing conclusions, they are conscious. And yet it's still a whole thing if various bugs of the world feel pain or if they are simply Instinct Machines that are Not Truly Aware of Anything At All????? Help!!!!!! How can you look at a little guy and think he is just the macroscopic animal version of a virus

Penis worms is serious business! been no-joke half-considering making an account to make a PSA about it (and other invertebrate stuff) for a while ^^; I like priapulids a lot, they’re a really underrated (and understudied) phylum

Hi, created an account just to let you know the photo you posted earlier is not a priapulid but a spawning sea cucumber, likely genus Paracaudina. It was misidentified on iNaturalist and went viral before it got corrected, and now it comes up on the search results along with a bunch of other worms like spoon and peanut worms that people misidentify as priapulids. The only priapulid that there’s good photos of is P. caudatus which is very distinctive if you know what it looks like. Love the blog!

Ah!!! Thank you very much for letting me know friend (even going as far as to make an account about it), sucks that these incorrect images have spread so far x(