Published on Archlosophy on 16 January 2026.
Critters
During a recent morning run along the river near my place, I came across these critters hanging around the sandstone banks. These sandstone blocks fronted the river and the banks, which were landscaped with native fauna. These critters resembled and behaved like a combination of insects I know of: a cockroach’s hurried, unpredictable movement, an isopod’s segmented shell, and a silverfish’s appearance. I managed to take a picture before it scuttled away into the crevices of the sandstone. Not knowing what to make of the critter, I consulted Chappie (ChatGPT) to identify the insect. Chappie told me it was a stonefly nymph, along with some of its characteristics.
Stonefly nymphs have two long tail filaments, whereas silverfish and mayfly nymphs usually have three. These nymphs’ flattened and elongated bodies allow them to cling to rocks in fast-moving waters, which is common among river-dwelling insect nymphs. While stonefly nymphs only have six legs, isopods have many, many more. So isopods are not regarded as insects. Lastly, stonefly nymphs live under rocks in oxygen-rich streams. They emerge when water levels change, or when they’re about to moult into adults, in the early morning and late evenings.
But Chappie also told me a cool fact- that stonefly nymphs are bioindicators. Since stonefly nymphs are sensitive and can only survive in pristine waters, their presence indicates the river ecosystem is healthy. That’s always a positive sign in any natural living system and reflects well on our stewardship of the environment. Turns out the river had more to teach me that morning.
Crabs
I also noticed these cool crabs burrowing in and out of the sand. The crabs were a near walk away from the location where I had found the stonefly nymphs. The crustaceans were dancing with death by coming out into the open, metres away from a river bird searching for a tasty snack! The crabs have different colours and sizes, which makes me believe they are of different species. It’s interesting to see them co-existing with each other in such proximity. I had assumed the crabs would be territorial. Armed with more questions, I had another chat with Chappie, and this was what I learned.
The crabs in the pictures are likely different species of intertidal crabs, namely the fiddler and sentinel crabs. The one with red colouration is the fiddler, and the sand coloured crab is the sentinel. Regarding coexistence among crabs, one reason is that they have different diets. Fiddler crabs filter feed on organic matter, algae, and microbes in the sand, whereas Sentinel crabs are more opportunistic, roaming around for detritus, small invertebrates, and biofilm.
In terms of their burrowed home, the depth, diameter, and moisture preference of the crabs need to be taken into consideration as well. While their burrows may be positioned close to each other, functionally they’re different. Being active in various conditions and having a predisposed behavioural trait also helps with co-existing. Think of it like living in an apartment block, but on different floors. Environmental factors such as low tide, sun/shade availability, and temperature reduce direct competition, as crabs have different preferences.
Furthermore, each of the crab’s predator avoidance strategies is different. Fiddlers rely on their visual awareness, retreating deep into their burrow at the slightest threat. Sentinels, on the other hand, rely on their ability to remain still and camouflage with their surroundings- in this case, with the sand. This behaviour was in line with what I had observed that day; it’s nice to get confirmation between theory and practice.
At least now I know that the river has a thriving ecosystem. Who knew watching these creatures could be calming?
This is another one of my postings in which I explicitly used artificial intelligence to augment my learning and satiate my curiosity. I guess what I’m suggesting is that AI, if used responsibly, can be a useful companion to our curiosity, as long as we remain attentive and critical of our surroundings. Hope you enjoyed learning something new today! Stay critterly crably curious!
Be kind to yourself,
Kai
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