Rarely-spotted larva known to few

• Published date: 06 November 2021
• Publication title: Mix, The

The adult beetle is rotund, flightless and 7mm long, with stout digging legs. It is very variable in colour, matching that of the sand in which it burrows. It feeds solely on cast-up seaweed, especially kelp, feeding 3cm to 15cm below the surface of the sand just above high tide level. Adult beetles are very common on most sandy marine beaches all around New Zealand, but larvae are only rarely seen, if at all. No-one knows why these larvae are so uncommon.

This beetle, Chaerodes trachyscelides, belongs to the family Tenebrionidae, or darkling beetles. When I made microscope slide preparations of the contents of the guts of both larvae and adults, and examined these under a high-powered microscope, I found numerous trumpet cells, used to transport photosynthesates through the blade and central parts of the stipe (stalk) of brown seaweed.

Most darkling beetle larvae are toughly sclerotised hard, straight, cylindrical false wireworms, like those of the large beetle, Mimopeus opaculus, common under old logs throughout much of New Zealand.

The larva of C. trachyscelides therefore comes as a surprise. It is white...