In the a recent Doctor Who episode, Arachnids in the UK, it is claimed that spiders never stop growing.
Is this true?
Tailless whip spiders (aka cave spiders or tailless whip scorpions) continue growing throughout their life:
No terminal molt takes place and so these animals grow all their life, but obviously the intervals between molts get longer in time. Both sexes have extremely elongated pedipalps, but the male's pedipalps are longer still.
They molt once or twice a year until they reach maturity. Tailless whip scorpions continue molting and growing throughout their adult lives.
Phrynichus jayakari Whip Spider
The order Amblypygi includes ca. 150 species and 17 genera within five families. Amblypygids are dorsoventrally flattened chelicerates with prominent raptorial pedipalps and chelate chelicerae. They are also the only arachnid order that lack an ultimate (= terminal) molt (Weygoldt 2002). The anteriormost legs of amblypygids are antenniform, being extremely long and whip-like (hence their common name, Whip Spiders)
Ecology and natural history of the tree-inhabiting social amblypygid Heterophrynus batesii