A moult is a full replacement of the exoskeleton, including the lining of the book lungs and the fangs. It is exhausting and it leaves the spider soft, defenceless and unable to move properly for hours. Almost everything a keeper can do during this period makes it worse.
Recognising pre-moult
- Refusing food, sometimes for weeks.
- Dull, faded colouring as the new exoskeleton forms underneath.
- A dark, shiny patch on the abdomen.
- Retreat sealed with fresh silk.
- Reduced movement, or long spells in the tunnel.
What to do
Remove live prey. Keep the water dish full. Keep the substrate damp, because a dry animal has a harder moult. Then leave the enclosure alone: no rehousing, no rearranging, no lifting the cork to check.
The moult itself
Arboreals often moult inside their web tunnel, hanging upside down. If you can see it happening, watch and do nothing. It can take from under an hour to most of a day. A spider that appears to be on its back is not dying, it is moulting.
Afterwards
The new exoskeleton is soft for several days. Do not feed until the fangs have darkened: about a week for a juvenile, up to two for a large adult. Do not rehouse for at least a fortnight. Do not handle at all, ever, but especially not now.
When it goes wrong
A stuck moult, where old exoskeleton remains attached to legs, is usually caused by an enclosure that was too dry. Raising humidity gently, by watering the substrate rather than misting the animal, is the only intervention worth attempting at home. Pulling at the old skin will remove legs.
Losing a leg is not fatal. Tarantulas regrow legs over the following moults, a little smaller at first, back to normal within two or three cycles.