Some 16km southwest of Otorohanga (8km west of SH3), WAITOMO is a diminutive village of under fifty inhabitants with an outsize reputation for incredible cave trips and magnificent karst features – streams that disappear down funnel-shaped sinkholes (Waitomo means “water entering shaft” in Maori), craggy limestone outcrops, fluted rocks, potholes and natural bridges caused by cave ceiling collapses. Below ground, seeping water has sculpted the rock into eerie and extraordinary shapes. The ongoing process of cave creation involves the interaction of rainwater and carbon dioxide from the air, which together form a weak acid. As more carbon dioxide is absorbed from the soil the acid grows stronger, dissolving the limestone and enlarging cracks and joints, eventually forming the varied caves you see today. Each year a further seventy cubic metres of limestone (about the size of a double-decker bus) is dissolved. Many of the caves are dazzlingly illuminated by glowworms.
The bulk of the caves are in (or visited from) Waitomo: for DIY limestone scenery sightseeing in any weather, head west to Mangapohue Natural Bridge and Piripiri Caves.
Local chief Tane Tinorau introduced Waitomo’s underground passages to English surveyor Fred Mace, in 1887. The pair explored further, building a raft of flax stems and drifting along an underground stream, with candles their only source of light. Within a year, the enterprising Tane was guiding tourists to see the spectacle. The government took over in 1906 and it wasn’t until 1989 that the caves were returned to their Maori owners, who receive a percentage of all revenue generated and participate in the site’s management.
Glowworms (Arachnocampa luminosa) are found all over New Zealand, mostly in caves but also on overhanging banks in the bush where in dark and damp conditions you’ll often see the telltale bluey-green glow. A glowworm isn’t a worm at all, but the matchstick-sized larval stage of the fungus gnat (a relative of the mosquito), which attaches itself to the cave roof and produces around twenty or thirty mucus-and-silk threads or “fishing lines”, which hang down a few centimetres. Drawn by the highly efficient chemical light, midges and flying insects get ensnared in the threads and the glowworm draws in the line to eat them.
The six- to nine-month larval stage is the only time in the glowworm life cycle that it can eat, so it needs to store energy for the two-week pupal stage when it transforms into the adult gnat that has no mouthparts. The gnat only lives a couple of days, during which time the female has to frantically find a mate in the dark caves (the glow is a big help here) and lay her batch of a hundred or so eggs. After a two- to three-week incubation, they hatch into glowworms and the process begins anew.