Care guide
The Silkworm Brain: What an Insect Uses to Think
A Brain Worth Studying
A silkworm is not usually thought of as having much of a nervous system. It has a well-characterised one, and it has been mapped down to cell types: Kenyon cells, optic lobe cells, monoaminergic neurons, surface glia and astrocyte glia.
Glia are the supporting cells around neurons, long assumed to be mere scaffolding and now known to do far more. Finding astrocyte-type glia in a moth is part of a broader story about how conserved these systems are.
The Mushroom Bodies
The structure that matters most here is the mushroom body — a paired region of the insect brain regarded as a centre for learning and memory. Kenyon cells are its principal neurons.
In the silk moth, olfactory information is carried to the mushroom body calyx and the lateral protocerebrum for second-order processing. In plain terms: a smell is detected at the antenna, and the signal is then handled by a structure whose job is interpretation rather than detection.
Why Smell Dominates
Because for this animal it is nearly everything. A male silk moth's entire adult existence is finding a female by scent — see bombykol, the first pheromone ever identified, and the receptor BmOR-1 expressed only in male antennae.
An animal that does not feed as an adult and cannot fly has one behavioural problem to solve, and its brain is built around solving it.
The Brain Is Rebuilt
The larval brain is not the adult brain. During metamorphosis the larval nervous system transforms into a mature adult version — the same animal, reorganised for a completely different life.
A caterpillar navigates leaf surfaces and decides when to moult. A moth navigates a scent plume and mates. One brain becomes the other inside the cocoon, which is among the more remarkable things happening in a structure people mostly think of as a source of thread.
Related: do silkworms need water? · the four silkworm diseases