A student of mine is researching scorpions and he has a question about emperor scorpions that we have been unable to answer through our own research. He has learned that baby emperor scorpions are born white, but he cannot find the answer to the question “WHY they are born white.” We would appreciate it very much if you knew and shared the answer.Bret, via Email
When scorpions are born, they’re ghostly pale. They actually stand out against their mom, looking almost more like maggots than actual arachnids.
But adult emporer scorpions, like mom up there, are dark. That darkness is an indicator of a hard exoskeleton, which scorpions need on their claws and stingers to crush and eat prey.
So why are they pale?
The first thing we need to understand is the molting process.
When an insect molts, there’s actually a lot going on. They more or less digest their exoskeleton from the inside, and squeeze out of what’s left. The bug under the exoskeleton is pale white, soft, and in this video, you can see how this cockroach is white just like the scorpion babies.
The stuff which makes arthropods dark is the same stuff which gives humans a darker complexion: melanin. The specifics of how it forms are VERY complicated, but in the end, it links proteins in the exoskeleton together to make the exoskeleton harder and inflexible. It also protects the critter from UV light. To allow insects the required time to escape the exoskeleton, melanin production can be delayed anywhere from a few hours to a few days while the bug hides out and hardens up. This process is called sclerotization.
Not all arthropods are heavily melanized, and baby emporer scorpions don’t turn super dark until somewhat late in life. Insects which live in dark, moist places tend to not be super melanized. Melanin is kind of problematic to produce, because some of it’s byproducts can be a bit toxic. So if you don’t need to make it, there’s no reason to.
A lot of arthropods navigate this trade-off by controlling where the melanin is made. Termites, for example, live their lives completely within wood. They rarely see light, so there’s no reason to make melanin. Except, they need hard mouthparts to eat wood.
Because they need hard mouthparts, but not a hard exoskeleton, termites make melanin on a specific part of their body…the mouthparts.
Emporer scorpions aren’t too different. They hide out for a good chunk of their lives, so they become gradually darker. However, when they’re old enough to leave mom, you can see slight bits of darker exoskeleton-sclerotization-on their claws.
Hopkins, T. L., & Kramer, K. J. (1992). Insect cuticle sclerotization. Annual review of entomology, 37(1), 273-302.
Kakkar, G., Chouvenc, T., & Su, N. Y. (2016). Postecdysis sclerotization of mouthparts of the Formosan subterranean termites (Isoptera: Rhinotermitidae). Journal of Economic Entomology, 109(2), 792-799.
Andersen, S. O. (2010). Insect cuticular sclerotization: a review. Insect biochemistry and molecular biology, 40(3), 166-178.